Cell search method, forward link frame transmission method, apparatus using the same and forward link frame structure

ABSTRACT

In a cellular system in which OFDM is used, a forward link synchronization channel, a common pilot channel structure, an initial cell searching method of a mobile station, and an adjacent cell searching method for handover are required. 
     A method of transmitting a forward synchronization signal in a wireless communication system according to the present invention includes generating a frame comprised of a plurality of sync blocks; and transmitting the frame through a forward link, wherein the frame comprises primary synchronization channel sequences which provide timing information of the sync blocks and a plurality of secondary synchronization channel sequences which provide timing information of the frame, wherein a cell identifier is specified by a combination of the primary synchronization channel sequence and a hopping code word specified by the plurality of the secondary synchronization channel sequences. Therefore, the cell searching time can be efficiently reduced in an OFDM system.

TECHNICAL FIELD

The present invention relates to an Orthogonal Frequency DivisionMultiplexing (OFDM) cellular system, and more particularly, to a methodof allocating a synchronization channel code for identifying a forwardlink cell in the OFDM cellular system, a method of transmitting aforward synchronization signal, a method of searching an initial celland an adjacent cell, and a mobile station, a base station, a system,and a frame structure using the methods.

BACKGROUND ART

In a Wideband Code Division Multiple Access (WCDMA) method, a systemuses 512 long PN scrambling codes and base stations, which are adjacentto each other, use long PN scrambling codes that are different to eachother as scrambling codes of forward link channels.

When a power source is applied to a mobile station, the mobile stationshould obtain a system timing of a base station (the base station havingthe largest reception signal) where the mobile station belongs to and along PN scrambling code ID (generally called a “cell identifier”). Thisprocess is referred to as a cell searching method of the mobile station.

In the WCDMA, 512 long PN scrambling codes are divided into 64 groups inorder to easily perform cell searching, and a primary synchronizationchannel and a secondary synchronization channel are placed in a forwardlink. The primary synchronization channel supports the mobile stationsto obtain slot synchronization and the secondary synchronization channelsupports the mobile station to obtain a 10 msec frame boundary and longPN scrambling code group ID information.

The cell searching method in the WCDMA method includes three processes.First, the mobile station obtains slot synchronization by using aPrimary Synchronization Channel Code (PSC). The same PSCs aretransmitted in 15 slot units for every 10 msec in the WCDMA method andthe PSCs transmitted by all base stations are the same. Therefore, inthe first process, slot synchronization is obtained by using a matchedfilter with respect to the PSC.

Second, the long PN scrambling code group information and the 10 msecframe boundary are obtained by using slot timing information obtainedfrom the first process and a Secondary Synchronization Channel Code(SSC).

Third, the long PN scrambling code ID currently used by the base stationis obtained by using a common pilot channel code correlator. Here, the10 msec frame boundary and the long PN scrambling code group informationobtained from the previous process are used. That is, 8 scrambling codesare mapped to one code group so that the mobile station compares 8outputs from the PN scrambling code correlator and detects the long PNscrambling code ID currently used by a cell.

The synchronization channel is basically classified into the primarysynchronization channel and the secondary synchronization channel in theWCDMA method, and the primary synchronization channel, the secondarysynchronization channel, a common pilot channel, and other data channelsare multiplexed using a CDMA method that is based on a time domaindirect sequence spread spectrum.

As a part of a 3G Long Term Evolution (3G-LTE) that is used as acomplement to the WCDMA method, Orthogonal Frequency DivisionMultiplexing (OFDM) based wireless transmission technologystandardization is now in progress. The synchronization channels, thecommon pilot channel structure, and the cell searching methods used inthe WCDMA method are suitable for a Direct Sequence-Code DivisionMultiple Access (DS-CDMA) and cannot be applied to the OFDM forwardlink.

Therefore, an adjacent cell searching method is required for thesynchronization channel of the forward link, the common pilot channelstructure, the initial cell searching method of the mobile station, andhandover in the OFDM based cellular system.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention provides a synchronization channel structure and aforward link frame so that a search process for an initial cell by amobile station and a search process for an adjacent cell for handovercan be easily performed in an Orthogonal Frequency Division Multiplexing(OFDM) cellular system.

The present invention also provides a method of allocating asynchronization channel code so that a search process for an initialcell by a mobile station and a search process for an adjacent cell forhandover in the OFDM cellular system.

The present invention also provides a cell searching apparatus and acell searching method including a search process for an initial cell bya mobile station and a search process for an adjacent cell for handoverin the OFDM cellular system.

The present invention also provides an apparatus for transmitting aforward link frame and a method thereof to support the cell searchingmethod.

The present invention also provides the OFDM cellular system to whichthe cell searching method is applied.

The present invention also provides a forward link frame structure inwhich the cell searching method is used.

The present invention also provides a computer readable recording mediumhaving embodied thereon a computer program executing the cell searchingmethod.

Technical Solution

According to an aspect of the present invention, there is provided amethod of transmitting a forward synchronization signal in a wirelesscommunication system, the method including: generating a frame comprisedof a plurality of sync blocks; and transmitting the frame through aforward link, wherein the frame comprises primary synchronizationchannel sequences which provide timing information of the sync blocksand a plurality of secondary synchronization channel sequences whichprovide timing information of the frame, wherein a cell identifier isspecified by a combination of the primary synchronization channelsequence and a hopping code word specified by the plurality of thesecondary synchronization channel sequences.

According to another embodiment of the present invention, there isprovided a method of transmitting a forward synchronization signal in awireless communication system, the method including: generating a framecomprised of a plurality of sync blocks; and transmitting the framethrough a forward link, wherein the frame comprises primarysynchronization channel sequences which provide timing information ofthe sync blocks and a plurality of secondary synchronization channelsequences which provide timing information of the frame and theplurality of the secondary synchronization channel sequences specifyhopping code words that are one-to-one mapped to cell identifiers.

According to another embodiment of the present invention, there isprovided a method of detecting cell identifiers by using a forwardsynchronization signal in a wireless communication system, the methodincluding: receiving a frame comprised of a plurality of sync blocks;extracting a sync block timing from primary synchronization channelsequence included in the frame, frame timing from a plurality ofsecondary synchronization channel sequences included in the frame, and ahopping code word specified by the plurality of the secondarysynchronization channel sequences; and detecting the cell identifier bycombination of the primary synchronization channel sequence and thehopping code word.

According to another embodiment of the present invention, there isprovided an apparatus for transmitting a forward synchronization signalin a wireless communication system, the apparatus including: a framegenerating unit generates a frame comprised of a plurality of the syncblocks, wherein the frame comprising primary synchronization channelsequences which provide timing information of sync blocks and aplurality of secondary synchronization channel sequences which providestiming information of the frame, wherein a cell identifier is specifiedby a combination of the primary synchronization channel sequence and ahopping code word specified by the plurality of the secondarysynchronization channel sequences; and a frame transmitting unittransmits the frame through a forward link.

According to another embodiment of the present invention, there isprovided an apparatus for transmitting a forward synchronization signalin a wireless communication system, the apparatus including: a framegenerating unit generates a frame comprised of a plurality of the syncblocks, wherein the frame comprising primary synchronization channelsequences which provide timing information of sync blocks and aplurality of secondary synchronization channel sequences which providetiming information of the frame, wherein the plurality of secondarysynchronization channel sequences specify hopping code words that areone-to-one mapped to cell identifiers; and a frame transmitting unittransmits the frame through a forward link.

According to another embodiment of the present invention, there isprovided a forward link frame comprised of a plurality of sync blocksused as a forward synchronization signal in a wireless communicationsystem, the forward link frame including: primary synchronizationchannel sequences which provide timing information of the sync blocksand a plurality of secondary synchronization channel sequences whichprovide timing information of the frame, wherein a cell identifier isspecified by a combination of the primary synchronization channelsequence and a hopping code word specified by the plurality of thesecondary synchronization channel sequences.

According to another embodiment of the present invention, there isprovided a forward link frame comprised of a plurality of sync blocksused as a forward synchronization signal in a wireless communicationsystem including: primary synchronization channel sequences whichprovide timing information of the sync blocks and a plurality ofsecondary synchronization channel sequences which provide timinginformation of the frame, wherein the plurality of secondarysynchronization channel sequences specify hopping code words that areone-to-one mapped to cell identifiers

ADVANTAGEOUS EFFECTS

According to the present invention, the cell searching time consumed bya mobile station can be reduced and a cell searching method that isperformed in a low-complexity can be executed in an Orthogonal FrequencyDivision Multiplexing (OFDM) cellular system.

Also, synchronization can be obtained with lower complexity by using amethod of transmitting a forward synchronization signal according to thepresent invention.

In addition, a search process for an adjacent cell can be efficientlyperformed by using the method of transmitting a forward synchronizationsignal according to the present in so that handover is smoothlyaccomplished and the battery consumption of the mobile station can bereduced.

Moreover, according to the method of transmitting a forwardsynchronization signal of the present invention, OFDM symbolsynchronization, a long scrambling code group ID, 10 msec frameboundary, and frequency offset can be estimated only with onesynchronization channel.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first method of allocating a code in a cellularsystem according to an embodiment of the present invention;

FIG. 2 illustrates a second method of allocating a code in a cellularsystem according to an embodiment of the present invention;

FIG. 3 illustrates a third method of allocating a code in a cellularsystem according to an embodiment of the present invention;

FIG. 4 illustrates a fourth method of allocating a code in a cellularsystem according to an embodiment of the present invention;

FIG. 5A illustrates a fifth method of allocating a code in a cellularsystem according to an embodiment of the present invention;

FIG. 5B illustrates a sixth method of allocating a code in a cellularsystem according to an embodiment of the present invention;

FIG. 6 illustrates a seventh method of allocating a code in a cellularsystem according to an embodiment of the present invention;

FIG. 7 illustrates a method of allocating cell identifiers to each cellwith respect to the first method of allocating a code in a cellularsystem according to an embodiment of the present invention;

FIG. 8 illustrates a forward link frame in which a primarysynchronization channel and a secondary synchronization channel areformed by Frequency Division Multiplexing (FDM);

FIG. 9 illustrates a forward link sub-frame in which a primarysynchronization channel and a secondary synchronization channel areformed by Frequency Division Multiplexing (FDM);

FIG. 10 illustrates a forward link frame in which a primarysynchronization channel and a secondary synchronization channel areformed by Time Division Multiplexing (TDM);

FIG. 11 illustrates a forward link sub-frame in which a primarysynchronization channel and a secondary synchronization channel areformed by Time Division Multiplexing (TDM);

FIGS. 12A and 12B are time domain concept diagrams of an OrthogonalFrequency Division Multiplexing (OFDM) symbol structure having a shortCP and a long CP, respectively;

FIG. 13 is concept diagram illustrating a phenomenon that a position ofa primary synchronization channel is changed according to a long CP anda short CP when a primary synchronization channel and a secondarysynchronization channel are formed by Time Division Multiplexing (TDM)and are present in a same sub-frame;

FIG. 14 illustrates a forward link frame in which a primarysynchronization channel is placed at the end of a sub-frame and asecondary synchronization channel is placed at the front of a nextsub-frame;

FIG. 15 is a concept diagram illustrating that there is a still timingambiguity on a secondary synchronization channel when a primarysynchronization channel and a secondary synchronization channel areplaced by Time Division Multiplexing (TDM) based on a sub-frameboundary;

FIG. 16 illustrates an example for explaining a method of resolving theproblem of FIG. 15 when the primary synchronization channel is placed atthe end of a sub-frame and the secondary synchronization channel isplaced at the front of a next sub-frame;

FIG. 17 illustrates an example for explaining a concept that thesecondary synchronization channel is formed by a cell common pilotsymbol and the FDM in a method of allocating the primary synchronizationchannel and the secondary synchronization channel of the presentinvention;

FIG. 18 is a concept diagram illustrating an occupied band of asynchronization channel when a system provides a scalable band width ina range of 1.25 MHz to 20 MHz;

FIG. 19 is a concept diagram of a transmitter in a base station whichintroduces switching diversity when there are two transmitting antennas;

FIG. 20 is a concept diagram of a receiver of a mobile station and acell searching unit according to an embodiment of the present invention;

FIG. 21 is a block diagram of a synchronization and group detecting unitof the cell searching unit of FIG. 20;

FIG. 22 is a concept diagram for explaining the operation of thesynchronization and group detecting unit of FIG. 21;

FIG. 23 is a concept diagram for explaining an input signal of a hoppingcode detecting unit of FIG. 20 when the primary synchronization and thesecondary synchronization channel are formed by FDM;

FIG. 24 is a concept diagram for explaining an input signal of a hoppingcode detecting unit of FIG. 20 when the primary synchronization and thesecondary synchronization channel are formed by TDM;

FIG. 25 is a block diagram of the hopping code detecting unit of FIG.20;

FIG. 26 is a block diagram of a sub-group and boundary detector of FIG.25;

FIG. 27 is a graph showing outputs of code correlation calculating unitsof FIG. 26;

FIG. 28 illustrates correlation values stored in a correlation buffer ofFIG. 26;

FIG. 29 is a block diagram of a cell identifier detecting unit of FIG.20;

FIG. 30 illustrates an operation of a pilot correlator according to anembodiment of the present invention;

FIG. 31 is a block diagram of a sub-group and a boundary detecting unitaccording to another embodiment of the present invention;

FIGS. 32A and 32B illustrate an operation of a home cell componentremoving unit; and

FIG. 33 illustrates a discontinuous reception (DRX) mode of a mobilestation during fine frequency tracking, fine time tracking, and adjacentcell searching of a home cell in an idle mode according to an embodimentof the present invention.

BEST MODE

According to an aspect of the present invention, there is provided amethod of transmitting a forward synchronization signal in a wirelesscommunication system, the method including: generating a frame comprisedof a plurality of sync blocks; and transmitting the frame through aforward link, wherein the frame comprises primary synchronizationchannel sequences which provide timing information of the sync blocksand a plurality of secondary synchronization channel sequences whichprovide timing information of the frame, wherein a cell identifier isspecified by a combination of the primary synchronization channelsequence and a hopping code word specified by the plurality of thesecondary synchronization channel sequences.

The hopping code word may select a part of the cell identifiers used inthe wireless communication system and the primary synchronizationchannel sequence may specify one cell identifier from among the part ofthe cell identifiers selected by the hopping code word.

Multiplication of the number of primary synchronization channelsequences and the number of the hopping code words may be the same asthe number of the cell identifiers used in the wireless communicationsystem.

The primary synchronization channel sequence may be selected from theplurality of the primary synchronization channel sequences used in thewireless communication system.

The primary synchronization channel sequence may be repeatedly locatedat the same position in each of the sync blocks in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a TDM method inadjacent symbol sections in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a FDM method in thesame symbol section in the frame.

According to another embodiment of the present invention, there isprovided a method of transmitting a forward synchronization signal in awireless communication system, the method including: generating a framecomprised of a plurality of sync blocks; and transmitting the framethrough a forward link, wherein the frame comprises primarysynchronization channel sequences which provide timing information ofthe sync blocks and a plurality of secondary synchronization channelsequences which provide timing information of the frame and theplurality of the secondary synchronization channel sequences specifyhopping code words that are one-to-one mapped to cell identifiers.

The primary synchronization channel sequence may be selected from theplurality of the primary synchronization channel sequences used in thewireless communication system and selects a part of the cell identifiersused in the wireless communication system.

The primary synchronization channel sequences may be repeatedly locatedat the same position in each of the sync blocks in the frame.

The primary synchronization channel sequences may be located at the sameposition in each of the sync blocks in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a TDM method inadjacent symbol sections in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a FDM method in thesame symbol section in the frame.

According to another embodiment of the present invention, there isprovided a method of detecting cell identifiers by using a forwardsynchronization signal in a wireless communication system, the methodincluding: receiving a frame comprised of a plurality of sync blocks;extracting a sync block timing from primary synchronization channelsequence included in the frame, frame timing from a plurality ofsecondary synchronization channel sequences included in the frame, and ahopping code word specified by the plurality of the secondarysynchronization channel sequences; and detecting the cell identifier bycombination of the primary synchronization channel sequence and thehopping code word.

The hopping code word may be used to select a part of the cellidentifiers used in the wireless communication system and the primarysynchronization channel sequence may be used to detect one cellidentifier from among the part of the cell identifiers selected by thehopping code word.

All primary synchronization channel sequences and all hopping code wordsused in the wireless communication system may be used to detect the cellidentifiers that are of the same number as a multiple of the number ofprimary synchronization channel sequences and the number of hopping codewords.

The primary synchronization channel sequence selected from a pluralityof the primary synchronization channel sequences used in the wirelesscommunication system may be used to detect the cell identifier.

According to another embodiment of the present invention, there isprovided an apparatus for transmitting a forward synchronization signalin a wireless communication system, the apparatus including: a framegenerating unit generates a frame comprised of a plurality of the syncblocks, wherein the frame comprising primary synchronization channelsequences which provide timing information of sync blocks and aplurality of secondary synchronization channel sequences which providestiming information of the frame, wherein a cell identifier is specifiedby a combination of the primary synchronization channel sequence and ahopping code word specified by the plurality of the secondarysynchronization channel sequences; and a frame transmitting unittransmits the frame through a forward link.

The hopping code word may select a part of the cell identifiers used inthe wireless communication system and the primary synchronizationchannel sequence may specify one cell identifier from among the part ofthe cell identifiers selected by the hopping code word.

Multiplication of the number of primary synchronization channelsequences and the number of hopping code words may be the same as thenumber of cell identifiers used in the wireless communication system.

The primary synchronization channel sequence may be selected from theplurality of the primary synchronization channel sequences used in thewireless communication system.

The primary synchronization channel sequence may be repeatedly locatedat the same position in each of the sync blocks in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a TDM method inadjacent symbol sections in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a FDM method in thesame symbol section in the frame.

According to another embodiment of the present invention, there isprovided an apparatus for transmitting a forward synchronization signalin a wireless communication system, the apparatus including: a framegenerating unit generates a frame comprised of a plurality of the syncblocks, wherein the frame comprising primary synchronization channelsequences which provide timing information of sync blocks and aplurality of secondary synchronization channel sequences which providetiming information of the frame, wherein the plurality of secondarysynchronization channel sequences specify hopping code words that areone-to-one mapped to cell identifiers; and a frame transmitting unittransmits the frame through a forward link.

The primary synchronization channel sequence may be selected from theplurality of the primary synchronization channel sequences used in thewireless communication system and may select a part of the cellidentifiers used in the wireless communication system.

The primary synchronization channel sequence may be repeatedly locatedat the same position in each of the sync blocks in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a TDM method inadjacent symbol sections in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a FDM method in thesame symbol section in the frame.

According to another embodiment of the present invention, there isprovided an apparatus of detecting cell identifiers using a forwardsynchronization signal in a wireless communication system, the apparatusincluding: a frame receiving unit which receives a frame comprised of aplurality of sync blocks; wherein a sync block timing is extracted fromprimary synchronization channel sequence included in the frame and aframe timing is extracted from a plurality of secondary synchronizationchannel sequences included in the frame, wherein a cell identifier isdetected by a combination of the primary synchronization channelsequence and a hopping code word specified by the plurality of thesecondary synchronization channel sequences.

The hopping code word may be used to specify a part of the cellidentifiers used in the wireless communication system and the primarysynchronization channel sequence may be used to detect one cellidentifier from among the part of the cell identifiers specified by thehopping code word.

The primary synchronization channel sequence and the hopping code wordused in the wireless communication system may be used to detect the cellidentifiers that are of the same number as a multiple of the number ofprimary synchronization channel sequences and the number of hopping codewords.

The primary synchronization channel sequence selected from a pluralityof the primary synchronization channel sequences used in the wirelesscommunication system may be used to detect the cell identifier.

According to another embodiment of the present invention, there isprovided a forward link frame comprised of a plurality of sync blocksused as a forward synchronization signal in a wireless communicationsystem, the forward link frame including: primary synchronizationchannel sequences which provide timing information of the sync blocksand a plurality of secondary synchronization channel sequences whichprovide timing information of the frame, wherein a cell identifier isspecified by a combination of the primary synchronization channelsequence and a hopping code word specified by the plurality of thesecondary synchronization channel sequences.

The hopping code word may be used to specify a part of the cellidentifiers used in the wireless communication system and the primarysynchronization channel sequence may be used to detect one cellidentifier from among the part of the cell identifiers specified by thehopping code word.

Multiplication of the number of primary synchronization channelsequences and the number of hopping code words may be the same as thenumber of cell identifiers used in the wireless communication system.

The primary synchronization channel sequence may be selected from theplurality of the primary synchronization channel sequences used in thewireless communication system.

The primary synchronization channel sequence may be repeatedly locatedat the same position in each of the sync blocks in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a TDM method inadjacent symbol sections in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a FDM method in thesame symbol section in the frame.

According to another embodiment of the present invention, there isprovided a forward link frame comprised of a plurality of sync blocksused as a forward synchronization signal in a wireless communicationsystem including: primary synchronization channel sequences whichprovide timing information of the sync blocks and a plurality ofsecondary synchronization channel sequences which provide timinginformation of the frame, wherein the plurality of secondarysynchronization channel sequences specify hopping code words that areone-to-one mapped to cell identifiers.

The primary synchronization channel sequence may be selected from theplurality of the primary synchronization channel sequences used in thewireless communication system and may select a part of the cellidentifiers used in the wireless communication system.

The primary synchronization channel sequence may be repeatedly locatedat the same position in each of the sync blocks in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a TDM method inadjacent symbol sections in the frame.

The primary synchronization channel sequences and the secondarysynchronization channel sequences may be located by a FDM method in thesame symbol section in the frame.

MODE OF THE INVENTION

A cell searching apparatus of a mobile station according to anembodiment of the present invention may be varied according to a methodof allocating a synchronization channel code of the present inventionwhich allows the mobile station to easily search for a cell in acellular system.

A synchronization channel is classified into a Primary SynchronizationChannel (P-SCH) and a Secondary Synchronization Channel (S-SCH). Themethod of allocating a synchronization channel code according to thepresent invention is a method which takes into account how the codesequences of the primary synchronization channel and the secondarysynchronization channel are allocated according to a cell identifier andmay be a kind of cellular code planning method.

Hereinafter, the method of allocating a synchronization channel code orthe cellular code planning method is simply referred to as a “method ofallocating a code.”

The method of allocating a code according to the present inventionintroduces a two-step grouping concept which divides the cellidentifiers used in a system into more than one cell group and divideseach of the cell groups again into more than one cell sub-group.

FIGS. 1 and 2 show examples of the method of allocating a codeillustrating a concept of a two-step cell grouping.

In other words, when it is assumed that 512 cell identifiers are presentin the system of FIGS. 1 and 2, each cell identifier is firstly dividedinto 8 cell groups 10, and then the 8 cell groups 10, which each include64 cell identifiers 40, are divided into 16 cell sub-groups 30. In thiscase, there are four cell identifiers in each of the cell sub-groups 30.

In the method of allocating a code in each cell of the cellular system,information about the cell groups 10 that corresponds to the cellidentifiers 40 allocated to each cell is sent through the primarysynchronization channel and information about the cell sub-groups 30 issent through the secondary synchronization channel.

FIG. 1 illustrates a first method of allocating a code in a cellularsystem according to an embodiment of the present invention.

In the first method of allocating a code in each cell of the cellularsystem according to the current embodiment of the present invention,sequences that have a one-to-one correspondence to the cell groups 10corresponding to the cell identifiers 40 allocated to each cell are usedas the primary synchronization channel sequence and hopping code wordsthat have a one-to-one correspondence to the cell sub-groups 30 are usedas hopping code words 20 of the secondary synchronization channel.

That is, the number of the primary synchronization channel sequencesused in the system is the same as the number of the cell groups and thenumber of the hopping code words of the secondary synchronizationchannel used in the system is the same as the number of the cellsub-groups 30.

In FIG. 1, the number of hopping code words is 128, as is the totalnumber of the cell sub-groups 30. The primary synchronization channelsequence and the hopping code words in the secondary synchronizationchannel will be described in more detail later.

FIG. 2 illustrates a second method of allocating a code in a cellularsystem according to an embodiment of the present invention.

In the second method of allocating a code in each cell of the cellularsystem according to the current embodiment of the present invention inFIG. 2, like the first method of allocating a code, sequences that havea one-to-one correspondence to the cell groups 10 corresponding to thecell identifiers 40 allocated to each cell are used as the primarysynchronization channel sequence. However, different hopping code wordsare used in a single cell group 10 as hopping code words 20 of thesecondary synchronization channel but the same hopping code words may bere-used in the other cell groups 10.

In this case, the number of the primary synchronization channelsequences used in the system is the same as the number of the cellgroups and the number of the hopping code words of the secondarysynchronization channel used in the system is the same as the valueobtained by dividing the number of cell sub-groups 30 into the number ofthe cell groups 10.

FIG. 3 shows an example in which there is one cell identifier per cellsub-group in the first method of allocating a code. This case does notdepart from the scope of the present invention. In this case, hoppingcode words of the secondary synchronization channel one-to-onecorrespond to the cell identifiers. For convenience, the caseillustrated in FIG. 3 is referred to as a “third method of allocating acode.”

According to the third method of allocating a code, the number of thecell identifiers is the same as the number of hopping code words of thesecondary synchronization channel, as the primary synchronizationchannel sequence designates a part of the cell identifiers, that is, apart of the hopping code words of the secondary synchronization channel.

For example, when the total number of cell identifiers is 128, the cellidentifiers are one-to-one mapped to the hopping code words of thesecondary synchronization channel and when the number of cell groups(that is, the primary synchronization channel sequence) is 8 as in FIG.3, each primary synchronization channel sequence selects 16 cellidentifiers, that is, 16 hopping code words in the secondarysynchronization channel.

In this case, a time domain correlation is performed with respect to aplurality of primary synchronization channel sequences in a first cellsearching process and information on the primary synchronization channelsequences is obtained as well as sync block synchronization. In a secondcell searching process, correlation is performed with respect to the 16hopping code words of the secondary synchronization channel selected bythe primary synchronization channel sequences obtained in the first cellsearching process and thus the cell identifiers are obtained.

As in FIG. 3, when the sequence number of the primary synchronizationchannel obtained in the first cell searching process is 4 (that is, thecell group number is 4), correlation is performed with respect to only16 hopping code words (that is, the hopping code words 64, 65, 66, . . ., 77, 78, 79 selected by the sequence number 4 of the primarysynchronization channel) among 128 hopping code words of the secondarysynchronization channel in the second cell searching process. Here,timing (boundary) information of a frame is obtained in the second cellsearching process.

FIG. 4 shows an example in which there is one cell identifier per cellsub-groups in the second method of allocating a code. This case does notdepart from the scope of the present invention. For convenience, thecase illustrated in FIG. 4 is referred to as a “fourth method ofallocating a code.”

According to the fourth method of allocating a code, the number of thecell identifiers can be allocated to be a multiplication of the numberof the primary synchronization channel sequences (cell groups) and thenumber of the hopping code words of the secondary synchronizationchannel.

For example, when the total number of the cell identifiers is 128, eachcell identifier can be expressed as a combination of 8 primarysynchronization channel sequences and 16 hopping code words of thesecondary synchronization channel (hopping code word identifiers) (thatis, 128=8×16).

In this case, all cell identifiers are classified into 8 groupsaccording to the primary synchronization channel sequences and eachgroup is comprised of 16 cell identifiers. Each group (cell groups) isspecified by each different primary synchronization channel sequence andthe cell identifiers included in each group can be allocated to beone-to-one mapped to hopping code words of the secondary synchronizationchannel (hopping code word identifiers).

Here, for each 16 cell identifier included in the cell groups, eachdifferent hopping code word identifiers of the secondary synchronizationchannel are used and for each 8 cell groups, the hopping code wordidentifiers of the secondary synchronization channel can be re-used.

In addition, as in FIG. 4, 8 cell identifiers among total of 128 cellidentifiers may be designated by the hopping code words (hopping codeword identifiers) and then 1 cell identifier among the 8 cellidentifiers may be finally specified by the primary synchronizationchannel sequence, since the same hopping code words are re-used in thecell groups 10 as in FIG. 2.

In this case, a time domain correlation is performed with respect to aplurality of primary synchronization channel sequences in a first cellsearching process and the sequence numbers of the primarysynchronization channel are obtained as well as sync blocksynchronization. Then, in a second cell searching process, a frameboundary and the hopping code word identifiers of the secondarysynchronization channel are obtained so that the cell identifiers thatare mapped to the sequence numbers of the primary synchronizationchannel obtained in the first cell searching process and the hoppingcode word identifiers of the secondary synchronization channel can bespecified.

Ultimately, a combination of the sequence numbers of the primarysynchronization channel and the hopping code word identifiers of thesecondary synchronization channel obtains cell identifiers.

FIG. 5A shows an example in which there is one cell group in the firstmethod of allocating a code. This case does not depart from the scope ofthe present invention. In this case, one primary synchronization channelsequence is used in the system. For convenience, the case illustrated inFIG. 5A is referred to as a “fifth method of allocating a code.”

FIG. 5B shows an example in which there is one cell group and one cellidentifier in the cell sub-group in the first method of allocating acode. This case does not depart from the scope of the present invention.In this case, one primary synchronization channel sequence is used inthe system and the number of hopping code words of the secondarysynchronization channel corresponds one-to-one to the number of the cellidentifiers. For convenience, the case illustrated in FIG. 5B isreferred to as a “sixth method of allocating a code.”

Additionally, in the case of fifth and sixth methods of allocating acode, the number of the cell groups is 1 so that the primarysynchronization channel sequence does not need to include information onthe cell groups. Also, the number of primary synchronization channelsequences can be different to the number of cell groups.

FIG. 6 shows another method of allocating a code according to anembodiment of the present invention in which the secondarysynchronization channel is not used. In this case, the cell identifiersare group only by cell group information of the primary synchronizationchannel. For convenience, the case illustrated in FIG. 6 is referred toas a “seventh method of allocating a code.”

As will be described later, in the seventh method of allocating a code,the cell searching apparatus of the mobile station obtainssynchronization of the sync block by using the primary synchronizationchannel and then directly obtains the cell identifiers and timing(boundary) information of a frame by using a common pilot signal (or areference signal) of a forward link.

In each of the cells in the cellular system, any one of the sevenmethods of allocating a code described above can be used and all cellsshould use the same method of allocating a code. That is, two arbitrarycells should not use the methods of allocating a code that are differentto each other.

FIG. 7 illustrates a method of allocating the cell identifiers to eachcell with respect to the first method of allocating a code according toan embodiment of the present invention.

Technologies to be described below can be applied to the second throughfourth methods of allocating a code,

In FIG. 7, the cell identifiers included in each different cell groupare allocated to two arbitrary adjacent cells. When the cell identifiersincluded in the same cell groups 10 are allocated to adjacent two cells,the primary synchronization channel sequences transmitted from two basestations are the same so that in the system, the timing may be uncertainin a synchronization mode of the base station in the first cellsearching process of the mobile station.

That is, multipath information obtained as a result of the first cellsearching process in which the mobile station uses the primarysynchronization channel sequence is the sum of the primarysynchronization channel sequences having the same sequences receivedfrom two adjacent base stations. Therefore, in the first or secondmethod of allocating a code which defines a plurality of the cell groups10, the cell identifiers included in each different cell group should beallocated to adjacent cells.

Different primary synchronization channel sequences are allocated toadjacent cells, since channel estimation values using the primarysynchronization channel sequences are used during coherent demodulatingof the secondary synchronization channel sequence in the second cellsearching process. In this case, when the primary synchronizationchannel sequences are the same in adjacent cells, detection probabilityfor the secondary synchronization channel sequences in the second cellsearching process can be reduced.

In the case of the fifth and sixth methods of allocating a code, thenumber of primary synchronization channel sequences does not need to bethe same as the number of the cell groups (1) so that a plurality of theprimary synchronization channel sequences is used and different primarysynchronization channel sequences are located in adjacent cells, therebyobtaining the same effect as above.

Meanwhile, when the number of the primary synchronization channelsequences (or the number of the cell groups) is less than 8, the primarysynchronization channel sequences (or the cell groups) are dispersedunder a fixed rule and can be allocated to each cell.

Since there is one cell group, if the number of primary synchronizationchannel sequences is 1, timing may be uncertain in the first cellsearching process. Therefore, in this case, a plurality of the primarysynchronization channel sequences can be allocated to each cell as inFIG. 7.

The present invention relates to a cell searching method includingsynchronization obtaining in the OFDM cellular system, timing (boundary)detecting, and cell identifiers detecting.

The term “synchronization obtaining” includes timing of synchronizationchannel symbol of the frame detecting, timing of sync block detecting,and boundary of sync block detecting and will be used in thisspecification.

The term “synchronization information” includes information on timing ofsynchronization channel symbol, timing of sync block, and boundary ofsync block and will be used in this specification.

The term “timing (boundary) of a frame detecting” indicates that timingof the frame boundary is detected and will be used in thisspecification.

The term “timing (boundary) information of a frame” includes informationon the timing of the frame boundary and will be used in thisspecification.

The term “cell group detecting” includes detecting the cell groupidentifiers and the cell groups and will be used in this specification.

The term “cell group information” includes information on the cell groupidentifiers and the cell groups and will be used in this specification.

The term “cell identifier detecting” includes detecting the cells orcell identifiers and will be used in this specification.

The “synchronization channel sequence” according to the presentinvention indicates a set of synchronization channel “chips” that aremapped to a subcarrier occupied by the synchronization channel symbol ina frequency domain. In the case of the primary synchronization channelsequences, the same sequences are used on each primary synchronizationchannel symbol. In the case of the secondary synchronization channel,each different sequence is used on each secondary synchronizationchannel symbol. The sequence number of the secondary synchronizationchannel used on each secondary synchronization channel symbol in theframe corresponds to element index corresponding to each symbol locationof the hopping code words allocated to the cells.

The hopping code words according to the present invention are M-aryhopping sequences used for sequence hopping of the secondarysynchronization channel sequences. In embodiments of the presentinvention, the length of the hopping code word is 5, the length of thehopping code word is the same as the number of synchronization channelsymbols per 10 msec frame, the number of values which can be held byeach element is 40 (that is, the size of alphabet of the hopping codeword M=40), and the number of secondary synchronization channelsequences given by each element of the hopping code word is the same asthe number of values (40) which can be held by each element of thehopping code word. In the base station, the same secondarysynchronization channel sequence hopping pattern, that is, the hoppingcode words, are used in each frame.

A set of the hopping code words used in the system is called a hoppingcode. Also, the hopping code word identifier numbers the hopping codewords and specifies information.

As in FIGS. 1, 3, and 5, when the number of hopping code words used inthe system is 128 and the number of synchronization channel symbols inthe frame is 5, the secondary synchronization channel sequence hoppingpattern with respect to each group, that is, hopping code word, isnumbered and the hopping code word identifiers are represented as in arange of integers of 0 to 127.

As in FIG. 2 or FIG. 4, when the number of hopping code words is 16, thehopping code word identifiers are represented by integers of 0 to 15.

For convenience, the term “Fourier Transform” is used in thisspecification to include discrete fourier transform and fast fouriertransform.

FIG. 8 illustrates a forward link frame in which the primarysynchronization channel and the secondary synchronization channel areformed by Frequency Division Multiplexing (FDM).

Referring to FIG. 8, each forward link frame has duration of 10 msec andis formed of 20 sub-frames 110. In FIG. 8, a horizontal axis is a timeaxis and a vertical axis is a frequency (OFDM subcarrier) axis.

The length of each sub-frame is 0.5 msec and 7 or 6 OFDM symbol sections120 are included in the sub-frames. When the number of symbols persub-frame is 6, the sub-frame can provide a service such as MultimediaBroadcast and Multicast Service (MBMS). In this case, the length ofcyclic prefix is greater than when the number of symbols per sub-framesis 7. Each sub-frame includes or does not include 1 synchronizationchannel symbol 100.

As in FIG. 8, one synchronization channel OFDM symbol section 100 existsin every four sub-frames and a total of 5 synchronization channel OFDMsymbol sections 100 exist in one frame (10 msec). In this case, arepetition cycle 140 of the synchronization channel symbol is the sameas the length obtained by adding four sub-frames so that the totalnumber of the repetition cycles 140 of the synchronization channelsymbols is 5. For convenience, a repetition cycle 140 of thesynchronization channel symbol is called a sync block 140.

That is, in FIG. 8, the number of sync blocks 140 in one frame (10 msec)is 5. The synchronization channel symbols can be located in anywhere inthe sync block 140, however, the location of the synchronization channelsymbol should be the same in each sync block.

In addition, as mentioned above, the number of symbols per sub-framescan be 6 or 7. In this case, in order to have no connection with thelength of cyclic prefix which may be different to each other, thelocation of the synchronization channel symbol should be at the end ofthe sub-frame. The detailed description thereof will be described later.

In FIG. 8, a cell's own scrambling codes are multiplied in a frequencydomain to distinguish each cell with respect to OFDM symbols except forthe synchronization channel symbol and the scrambling code numbers whichare one-to-one mapped to the cell identifiers.

FIG. 9 illustrates a forward link sub-frame including thesynchronization channel symbol in which the primary synchronizationchannel and the secondary synchronization channel are formed byFrequency Division Multiplexing (FDM).

According to the sub-frame of FIG. 9, a first OFDM symbol section 130-Aand a fifth OFDM symbol section 130-B include a pilot subcarrier 210 anda data subcarrier 220 in a FDM form. The last symbol section 100includes primary and secondary synchronization channel subcarriers 230and 240, synchronization channel guard bands 201-A and 201-B, and thedata subcarrier 220 in a FDM form.

For convenience, the first OFDM symbol section 130-A and the fifth OFDMsymbol section 130-B including the pilot subcarrier 210 are called apilot symbol section and the last symbol section 100 including theprimary and secondary synchronization channel subcarriers 230 and 240 iscalled a synchronization channel symbol section.

In the remaining symbol section except for the pilot symbol sections130-A and 130-B and the synchronization channel symbol section 100, adata subcarrier 220 is transmitted. In the case of the sub-frames inwhich the synchronization channel symbol section is not included, onlythe data subcarrier 220 is transmitted in the last sub-frame.

As shown in FIG. 9, a synchronization channel occupied band 200 isformed of the primary and secondary synchronization channel subcarriers230 and 240 and the synchronization channel guard bands 201-A and 201-Band uses only a part of the whole system bandwidth 310. The detaileddescription thereof will be mentioned later.

Referring to FIG. 9, the synchronization channel which uses one OFDMsymbol section from among various OFDM symbol sections in the sub-framedivides the part where the synchronization channel guard bands 201-A and201-B are excluded in the synchronization channel occupied band 200 intothe primary synchronization channel and the secondary synchronizationchannel in a FDM form.

FIG. 9 is an example of the FDM method. When total number of subcarriersallocated to the synchronization channel is 75, except for a DCsubcarrier, 37 subcarriers are allocated to the primary synchronizationchannel and 38 subcarriers are allocated to the secondarysynchronization channel.

In FIG. 9, a^((g))=[a^((g)) ₀, a^((g)) ₁, a^((g)) ₂, . . . , a^((g)) ₃₆]indicates the primary synchronization channel sequence that correspondsto g that is the cell groups number 10 described while defining thefirst through sixth method of allocating a code above.

The elements of the primary synchronization channel sequence, that is,a^((k)) ₀, a^((k)) ₁, a^((k)) ₂, . . . , a^((k)) ₃₆, have complex valuesor real number values and are allocated to the primary synchronizationchannel subcarrier 230 to be transmitted as illustrated in FIG. 9.

An arbitrary sequence can be used as the primary synchronization channelsequence, however, autocorrelation and cross correlation thereof shouldbe excellent when the primary synchronization channel sequence ischanged to a time domain signal.

The time domain signal component of the primary synchronization channelsequence may have complex values or real number values. The sequencesthat are different to each other in the primary synchronization channelsequence are allocated by each cell group and the same sequences areused on the synchronization channel symbol in all sync blocks in allframes transmitted to the forward link.

A receiver of a mobile station can introduce an accumulation technologyby using the characteristic of the primary synchronization channel inorder to obtain synchronization of the sync block 140 in the first cellsearching process. This will be described more fully later.

Meanwhile, in FIG. 9, C^((k))=[c^((k)) ₀, c^((k)) ₁, c^((k)) ₂, . . . ,c^((k)) ₃₇] indicates the secondary synchronization channel sequence inwhich the element index of the hopping code words corresponding to thesynchronization channel symbol is “k”.

The elements of the secondary synchronization channel sequence, that is,c^((k)) ₀, c^((k)) ₁, c^((k)) ₂, . . . , c^((k)) ₃₇, may have complexvalues or real number values and are allocated to the secondarysynchronization channel subcarrier 240 to be transmitted as illustratedin FIG. 9.

An arbitrary sequence can be used as the secondary synchronizationchannel sequence. Here, Generalized Chirp Like (GCL) sequence defined asin Equation 1 can be used.

$\begin{matrix}{{C_{n}^{(k)} = {\exp \left\{ {{- j}\; 2{\pi \left( {k + 1} \right)}\frac{n\left( {n + 1} \right)}{2\; N}} \right\}}},{n = 0},1,2,{{\ldots \mspace{14mu} N} - 1},,\mspace{14mu} {k = 0},1,2,\ldots \mspace{14mu},{N - 2}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, k is given by arbitrary index of elements of the hopping codewords and is referred to as the secondary synchronization channelsequence number. c^((k)) _(n) indicates n^(th) element of the secondarysynchronization channel sequence having the sequence number of k.

N is a length of the GCL sequence. In particular, each code length N inthe GCL sequence is a prime number and total of N−1 sequences exist.

That is, when the GCL sequence is used, a set of the GCL sequence usedin the system includes N−1 GCL sequences. In addition, the number of GCLsequences is the same as the size of alphabet of the hopping code words.The size of alphabet of the hopping code words will be described later.

The GCL sequence defined by Equation 1 is only an example of a sequencewhich can be used as the secondary synchronization channel sequence, andother sequences except for the GCL sequence, for example, a Goldsequence, a longest sequence, or a combination thereof can be used.

Meanwhile, except for the DC subcarrier, the number of subcarriers inthe synchronization channel occupied band is 75. When 38 subcarriersfrom among 75 subcarriers are used as the secondary synchronizationchannel in the FDM method of FIG. 8, 38 carriers can be allocated.

In this case, since 38 is not a prime number, any one number that is thesame or greater than 38 should be used as N which is the length of theGCL sequence. In the current embodiment, N is 41.

In FIG. 9, the number of secondary synchronization channel subcarriersis 38 and is less than the number of GCL sequence, 41, so that the lastthree chips among 41 are not transmitted.

The secondary synchronization channel sequences that correspond to eachof the secondary synchronization channel symbols in the frame arespecified by the element index of the hopping code words. That is, thesecondary synchronization channel sequences in the frame are formed in asequence hopping form.

In other words, the base station maps each of the hopping code wordelements onto each of the synchronization channel symbols in the frameso that the GCL sequence designated by the element index is allocated tothe secondary synchronization channel sequence of the correspondingsynchronization channel symbol to be transmitted. The mobile stationdetects the hopping code word identifiers (numbers) implied in thesynchronization channel symbols that is transmitted by a target basestation.

Here, examples of the target base station include a base station that issearched by the mobile station at an initial stage and an adjacent basestation to be searched for handover.

In table 1 below, the number of hopping code words used in the system asin FIGS. 1, 3, and 5 is 128, the number of synchronization channelsymbols in the frame is 5, and the secondary synchronization channelsequence hopping pattern with respect to each code group, that is, a setof the hopping code words is illustrated.

That is, 128 hopping pattern can be represented as a hopping code wordhaving the length of 5 and the length of the hopping code word is thesame as the number of synchronization channel symbols per 10 msec frame.A total set of hopping code words is defined as the hopping code.

As in FIG. 2 or FIG. 4, when the number of hopping code words is 16,only 16 hopping code words among 128 in Table 1 are used. Meanwhile, thebase station uses the same synchronization channel hopping pattern(hopping code word) in each frame.

In the case of the first method of allocating a code in FIG. 1 and thefifth method of allocating a code in FIG. 5, the hopping code words thatare different to each other are allocated according to the cellsub-groups 30. In the case of the third method of allocating a code inFIG. 3 and the sixth method of allocating a code in FIG. 5B, the hoppingcode words that are different to each other are allocated according tothe cell identifiers.

On the other hand, in the second method of allocating a code in FIG. 2and the fourth method of allocating a code in FIG. 4, the same hoppingcode words can be allocated to each different cell sub-groups or eachdifferent cell identifiers.

Meanwhile, in the seventh method of allocating a code in FIG. 6, thesecondary synchronization channel is not transmitted so that the hoppingcode defined in Table 1 cannot be used.

Referring to table 1, each of the hopping code words is formed of fivehopping code word elements. When there are four synchronization channelsymbol section 100 per frame, the length of the hopping code words, thatis, the number of elements, is 4.

Table 1 is only an example of the hopping codes and a Reed-Solomon (RS)code also can be used as the hopping codes.

TABLE 1 hopping code word identifiers 0 4, 5, 6, 7, 8 1 9, 10, 11, 12,13 2 14, 15, 16, 17, 18 3 19, 20, 21, 22, 23 4 24, 25, 26, 27, 28 5 29,30, 31, 32, 33 6 34, 35, 36, 37, 38 7 0, 2, 4, 6, 39 8 35, 38, 0, 29, 329 33, 36, 39, 1, 4 10 5, 9, 13, 38, 1 11 6, 12, 29, 35, 0 12 36, 1, 18,24, 30 13 7, 13, 19, 25, 31 14 2, 8, 14, 20, 37 15 26, 32, 38, 3, 9 1621, 27, 33, 39, 15 17 16, 22, 28, 4, 10 18 32, 3, 37, 8, 20 19 38, 31,2, 14, 26 20 20, 34, 7, 33, 6 21 9, 11, 13, 15, 17 22 19, 21, 23, 25, 2723 29, 31, 33, 35, 37 24 8, 10, 12, 14, 16 25 18, 20, 22, 24, 26 26 28,30, 32, 34, 36 27 14, 17, 20, 23, 26 28 3, 6, 9, 12, 15 29 18, 21, 24,27, 30 30 7, 10, 13, 16, 19 32 19, 23, 27, 31, 35 33 39, 2, 6, 10, 14 3418, 22, 26, 30, 34 35 17, 21, 25, 29, 33 36 37, 0, 4, 8, 12 37 16, 20,24, 28, 32 38 24, 29, 34, 39, 3 39 8, 13, 18, 23, 28 40 33, 38, 2, 7, 1241 17, 22, 27, 32, 37 42 1, 6, 11, 16, 21 43 26, 31, 36, 0, 5 44 10, 15,20, 25, 30 45 34, 0, 7, 14, 21 46 28, 35, 1, 8, 15 47 22, 29, 36, 2, 948 16, 23, 30, 37, 3 49 10, 17, 24, 31, 38 50 4, 11, 18, 25, 32 51 39,5, 12, 19, 26 52 39, 6, 14, 22, 30 53 38, 5, 13, 21, 29 54 37, 4, 12,20, 28 55 36, 3, 11, 19, 27 56 35, 2, 10, 18, 26 57 34, 1, 9, 17, 25 5833, 0, 8, 16, 24 59 18, 30, 1, 13, 25 60 15, 27, 39, 10, 22 61 34, 5,17, 29, 0 62 12, 24, 36, 7, 19 64 28, 1, 15, 29, 2 65 16, 30, 3, 17, 3166 4, 18, 32, 5, 19 67 21, 35, 8, 22, 36 68 9, 23, 37, 10, 24 69 38, 11,25, 39, 12 70 33, 7, 22, 37, 11 71 26, 0, 15, 30, 4 72 19, 34, 8, 23, 3873 12, 27, 1, 16, 31 74 5, 20, 35, 9, 24 75 39, 13, 28, 2, 17 76 32, 6,21, 36, 10 77 14, 35, 15, 36, 16 78 3, 27, 34, 23, 8 79 35, 17, 16, 6,25 80 3, 32, 25, 33, 5 81 24, 20, 27, 0, 13 82 31, 0, 16, 27, 5 83 23,0, 22, 2, 3 84 36, 33, 16, 25, 2 85 25, 11, 37, 26, 10 86 11, 26, 24, 6,17 87 28, 18, 2, 37, 21 88 0, 33, 37, 13, 30 89 22, 32, 13, 0, 38 90 34,11, 21, 5, 14 91 12, 4, 14, 23, 33 92 29, 11, 4, 17, 5 93 9, 1, 39, 28,7 94 18, 15, 2, 23, 31 96 5, 22, 8, 33, 15 97 19, 37, 28, 29, 6 98 1,26, 20, 11, 14 99 6, 5, 39, 38, 27 100 37, 39, 35, 13, 17 101 1, 24, 3,29, 15 102 10, 30, 25, 5, 28 103 7, 29, 16, 15, 22 104 37, 23, 11, 2, 29105 19, 14, 12, 39, 30 106 34, 33, 20, 1, 23 107 21, 8, 7, 6, 27 108 17,26, 3, 8, 32 109 17, 35, 22, 12, 7 110 15, 35, 14, 27, 25 111 31, 37, 9,6, 1 112 26, 4, 23, 1, 32 113 32, 12, 18, 29, 21 114 30, 17, 38, 15, 37115 33, 22, 6, 24, 13 116 4, 38, 33, 8, 34 117 27, 37, 33, 32, 10 11813, 2, 11, 35, 34 119 15, 14, 11, 7, 37 120 29, 1, 27, 2, 38 121 38, 16,39, 29, 9 122 9, 36, 24, 17, 28 123 4, 0, 25, 9, 39 124 8, 21, 11, 1, 20125 4, 36, 14, 13, 31 126 39, 7, 25, 36, 32

In the table above, the alphabet size of the hopping code is 40. Thatis, the hopping code element k that is mapped to the secondarysynchronization channel sequence in each sync block is any number from 0to 39.

For example, assuming that the first method of allocating a code is usedin the system.

When the cell identifier of the current base station is 0, the cellidentifier is included in cell sub-group 0 as in FIG. 1 and the hoppingcode words allocated to the cell sub-group 0 are {4, 5, 6, 7, 8} as inTable 1.

Ultimately, five secondary synchronization channel symbols transmittedper frame by the current base station have the hopping code wordelements that are 4, 5, 6, 7, and 8, and values defined by Equation 1are allocated to the subcarriers used by each of the synchronizationchannel symbols according to the hopping code word element index k. Inparticular, FIG. 1 shows an example when the code group identifier ofthe current base station is 0.

The 128 hopping code words are each different and are unique to allcyclic shifts. The hopping code words corresponding to code group 0 are{4, 5, 6, 7, 8} and the cyclic shifted pattern of the hopping code wordsare {5, 6, 7, 8, 4}, {6, 7, 8, 4, 5}, {7, 8, 4, 5, 6}, {8, 4, 5, 6, 7}.

Table 2 shows the cyclic shifted pattern of the hopping code words {4,5, 6, 7, 8} and a cyclic shift index.

TABLE 2 i-th cyclic shifted pattern cyclic shift index 0 cyclic shiftedsequence = 4, 5, 6, 7, 8 0 1 cyclic shifted sequence = 5, 6, 7, 8, 4 1 2cyclic shifted sequence = 6, 7, 8, 4, 5 2 3 cyclic shifted sequence = 7,8, 4, 5, 6 3

The number of hopping code words which can be obtained by using 128hopping code words and the cyclic shifted pattern of the hopping codewords is 640(=5×128) and each of the hopping code words are unique.

That is, as illustrated in Table 1, the same sequence does not exist inall code words which can be obtained by using the hopping code words andthe cyclic shifted pattern of the hopping code words used in the systemfor sequence hopping of the secondary synchronization channel.Uniqueness of all cyclic shifted hopping code words helps the mobilestation to obtain information on the code groups in the second cellsearching process and the 10 msec frame boundary.

The hopping codes according to the present invention may use hoppingcode sequences that are restricted by the number of clashes. Here, aclash means that elements of two arbitrary code words are the same.

For example, in Table 1, the elements of the hopping code words withidentifier number 0, that is, 4, 5, 6, 7, 8, are different from theelements of the hopping code words with identifier number 7, that is, 0,2, 4, 6, 39. In other words, the clash is “0.”

On the other hand, when the hopping code word identifier with number 7are shifted by 2, 2 cyclic shifted sequence, that is, {4, 6, 39, 0, 2}clashes with the first element of the hopping code words {4, 5, 6, 7, 8}having the identifier number 0, that is, 4. In this case, the number ofclashes is “1.”

The number of clashes between the code words is related to a hammingdistance.

For example, since the clash between two code words is “0,” the hammingdistance between two code words is the same as the sequence length (5 inTable 1). Accordingly, the number of clashes between two arbitrary codewords is the same as the value in which the hamming distance issubtracted from the length of the code word. In Table 1, the minimumhamming distance between all cyclic shifted code words (that is, 640code words) is 4.

In other words, the maximum number of clashes between arbitrary cyclicshifted code words is 1 or less. Accordingly, Equation 2 below isformed.

Minimum hamming distance=(length of the hopping code)−(clash of thehopping codes)  [Equation 2]

In the present invention, the hopping codes can include all cyclicshifted code words so that the number of clashes between two code wordscan be restricted. In other words, the minimum hamming distance can berestricted, for example, in the case when the terminal of the mobilestation is applied to a dual mode terminal which simultaneously providesGlobal System for Mobile Communication (GSM) and the OFDM system.

In this case, in handover from GSM to the OFDM system, the clash of thehopping codes (that is, the number of clash between 640 cyclic shiftedcode words is less than 1, i.e., the minimum hamming distance is 4)helps the dual mode terminal to detect 10 msec frame synchronization andhopping code identifiers, even by using two synchronization channelsymbols.

That is, the mobile station which demodulates the GSM forward link stopsthe GSM forward link for a while and receives a forward link signal ofanother system of another frequency. Accordingly, the cell searchingtime is approximately 4.6 msec.

When a GSM terminal receives a forward link signal during this time, thenumber of synchronization channel symbols which can be entered within4.6 msec is 2 or 3 in the frame of FIG. 8. That is, the worst case is 2.

Ultimately, the dual mode terminal should receive only 2 synchronizationchannel symbols and detect 10 msec frame synchronization and the hoppingcode identifiers. However, when the number of clashes between all cyclicshifted code words of the hopping code words is greater than 2, 10 msecframe synchronization and the code groups cannot be detected.

Accordingly, when the length of the hopping code is 5 as in Table 1(that is, when the number of secondary synchronization channel symbolsper frame is 5), the maximum number of clashes between all cyclicshifted code words of the hopping code words should be less than 1 sothat cell can be searched from GSM to the OFDM system and handover ispossible.

When the number of synchronization channel symbols per 10 msec frame is4 (that is, when the length of the hopping code is 4), the number ofsymbols which can be entered within 4.6 msec in FIG. 8 is 1 at theworst.

In this case, the maximum number of clashes between the cyclic shiftedcode words should be 0 (that is, the minimum hamming distance should bethe same as the length of the hopping code, 4).

When the number of synchronization channel symbols per 10 msec frame is10 (that is, when the length of the hopping code is 10), the number ofsymbols which can be seen within 4.6 msec in FIG. 8 is 4 at the worst.In this case, the maximum number of clashes between the cyclic shiftedcode words should be 3 (that is, the minimum hamming distance should be7).

Ultimately, when the minimum number of the synchronization channelsymbols which can be received during 4.6 msec transmission gap of GSM(In the case of the TDM method of FIG. 10, the number of secondarysynchronization channel symbols) is Q, the maximum number of clashesbetween arbitrary cyclic shifted hopping code words of the hopping codesshould be less than Q−1.

In other words, when the length of the hopping code is L, the minimumhamming distance should be greater than L−Q+1.

When the number of clashes between all cyclic shifted code words of thehopping code words is 0, the hopping code words and the frame boundarycan be obtained by using only one secondary synchronization channelsymbol. Accordingly, the case when the number of clashes between thecyclic shifted code words is 0 does not depart from the scope of thepresent invention.

In this case, the secondary synchronization channel sequence does notcorrespond to each sync block and each different sub-group.

FIG. 10 illustrates a forward link frame in which the primarysynchronization channel and the secondary synchronization channel areformed by Time Division Multiplexing (TDM).

The concept of the TDM which performs sequence hopping to the secondarysynchronization channel is the same as that of the FDM in FIG. 8. Thedifference from the FDM method is, a primary synchronization channelsymbol 160 and a secondary synchronization channel symbol 170 occupydifferent locations in the TDM as shown in FIG. 10.

In TDM, in the case of the primary synchronization channel, all occupiedbands can be used or only odd number subcarriers can be used as in FIG.11. When only odd number subcarriers are used as in FIG. 11 (or whenonly even number subcarriers are used), a repeated pattern is given to atime domain signal so that a differential correlator having a simplestructure can be used, in addition to a parallel correlator in a replicamethod, in the first cell searching process. The detailed descriptionwill be described later.

Also in TDM, elements of the primary synchronization channel sequence,that is, a^((k)) ₀, a^((k)) ₁, a^((k)) ₂, . . . , a^((k)) ₃₇, havecomplex values or real number values and are allocated to the primarysynchronization channel subcarrier 260 to be transmitted as illustratedin FIG. 11.

An arbitrary sequence can be used as the primary synchronization channelsequence, however, autocorrelation and cross correlation thereof shouldbe excellent when the primary synchronization channel sequence ischanged to a time domain signal.

The time domain signal component of the primary synchronization channelsequence may have complex values or real number values.

The sequences that are different to each other in the primarysynchronization channel sequence are allocated to each cell group andthe same sequences are used on the primary synchronization channelsymbol 160 in all sync blocks in all sync blocks 140 of all frametransmitted to the forward link.

A receiver of a mobile station can introduce an accumulation technologyby using the characteristic of the primary synchronization channel inorder to obtain synchronization of the sync block 140 in the first cellsearching process. This will be described more fully later.

Meanwhile, in FIG. 11, C^((k))=[c^((k)) ₀, c^((k)) ₁, c^((k)) ₂, . . . ,c^((k)) ₇₄] indicates the secondary synchronization channel sequence inwhich the element index of the hopping code words corresponding to thesynchronization channel symbol is “k”.

The elements of the secondary synchronization channel sequence, that is,c^((k)) ₀, c^((k)) ₁, c^((k)) ₂, . . . , c^((k)) ₇₄, may have complexvalues or real number values and are allocated to the secondarysynchronization channel subcarrier 270 to be transmitted as illustratedin FIG. 11.

An arbitrary sequence can be used as the secondary synchronizationchannel sequence. Here, Generalized Chirp Like (GCL) sequence defined asin Equation 1 can be used.

The GCL sequence defined by Equation 1 is only an example of a sequencewhich can be used as the secondary synchronization channel sequence, andother sequences except for the GCL sequence, for example, a Goldsequence, a longest sequence, or a combination thereof can be used.

Meanwhile, the OFDM system defines two types of sub-frames. One is tomainly provide unicast service and the other one is to mainly provideMBMS service.

The sub-frame to provide unicast service has 7 OFDM symbols persub-frame and the sub-frame to provide MBMS service has 6 OFDM symbolsper sub-frame.

In both cases, the lengths of CPs are different to each other. FIGS. 12Aand 12B are time domain concept diagrams of OFDM symbol having a shortCP and a long CP, respectively. The lengths of remaining parts 320 and330 except for the CPs are same, regardless of the length of the CP.

When there are 7 symbols per sub-frame, the short CP as in FIG. 12A isused and when there are 6 symbols per sub-frame, the long CP as in FIG.12B is used. However, in the OFDM system, the sub-frame having a shortCP and the sub-frame having a long CP can co-exist in a 10 msec frame.

When the primary synchronization channel and the secondarysynchronization channel are combined with the FDM method as in FIG. 8,one synchronization channel symbol is transmitted to the sub-frame wherethe synchronization channel exists. Therefore, as mentioned above, whenthe synchronization channel is placed at the end of the sub-frame, thelengths of the remaining parts 320 and 330 except for the CPs are same,even of the lengths of the CPs per sub-frame are different, so that themobile station can easily search for a cell.

However, as in FIG. 11, when the primary synchronization channel and thesecondary synchronization channel co-exist in one frame and areclassified by the TDM, the current frame has different starting pointsfor the primary synchronization channel symbol in the frame having along CP and in the frame having a short CP as in FIG. 13. Therefore, aswill be described later, timing ambiguity for sync block boundarydetecting occurs in the first cell searching process and theaccumulation technology which can improve the performance of the firstcell searching process cannot be introduced.

In the method of combining the primary synchronization channel and thesecondary synchronization channel with the FDM method according to thepresent invention, there are two methods to solve such problems.

One is for all OFDM symbols to have the same CP lengths in thesub-frames (that is, sub-frames 3, 7, 11, 15, and 19 in FIG. 10)simultaneously including the primary synchronization channel andsecondary synchronization channel. According to the method, allsub-frames have all short CP or all long CP.

The other one is for the primary synchronization channel 160 to beplaced at the end of the sub-frame and for a secondary synchronizationchannel symbol 360 to be placed at the front of the next sub-frame as inFIG. 14.

In this case, a time domain synchronization channel is available at aboundary 370 between the sub-frame where the primary synchronizationchannel is placed and the sub-frame where the secondary synchronizationchannel is placed. A concept diagram of the time domain synchronizationchannel is illustrated in FIG. 15.

Here, the primary synchronization channel symbol section except for theCPs constantly exists at a fixed location, regardless of the length ofthe CP. In this case, the timing ambiguity is removed in the first cellsearching process so that an accumulation technology can be introduced.On the other hand, in the case of the secondary synchronization channel,the location of the secondary synchronization channel symbol except forthe CP can be changed according to the length of the CP as in FIG. 15.

In this case, timing ambiguity may occur in the second cell searchingprocess where the secondary synchronization channel is used. The methodof solving this problem is to insert a postfix 390 into a first symbolof the sub-frame having long CP as in FIG. 16 when the secondarysynchronization channel is placed at the first symbol of the sub-framehaving long CP.

Here, the locations of the secondary synchronization channel symbolsections except for the CPs and postfix 390 are the same, regardless ofthe sub-frames having long CP or short CP, so that timing ambiguity canbe solved.

As in FIG. 14, in the TMD method of the present invention in which theprimary synchronization channel is placed at the end of the sub-frameand the secondary synchronization channel is placed at the first of thesub-frame, the first symbol section of the sub-frame where the secondarysynchronization channel is placed is where a common pilot symbol exists.

The common pilot symbol is a common channel used for channel estimationto coherently demodulate data channel of a forward link so that thesecondary synchronization channel should not occupy the location of thesubcarrier used by the common pilot symbol.

FIG. 17 illustrates that the secondary synchronization channel formed bythe FDM method in a synchronization channel band between a pilotsubcarrier and the secondary synchronization channel subcarrier when thesecondary synchronization channel is placed at the first symbol of thesub-frame.

Meanwhile, according to the method of allocating the synchronizationchannel occupied band, the synchronization channel may occupy only apart of a whole band allocated to the system. Examples of system towhich the above method can be applied include the OFDM system whichshould provide a scalable bandwidth.

That is, in order for all mobile stations using 1.25 MHz, 2.5 MHz, and 5MHz, 10 MHz, 15 MHz, and 20 MHz, respectively, to obtain synchronizationof the base station system, the synchronization channel symbolsrespectively occupy only a part of a whole system bandwidth 310 asillustrated in FIG. 18.

For example, when the system bandwidths are 1.25, 2.5, 10, and 15 MHz,the bandwidth of 1.25 MHz in the middle is only used. When the systembandwidth is 20 MHz, the minimum band of the mobile station is 10 MHz.Accordingly, in order to search for adjacent base station withoutcutting off during telephoning, two synchronization channel bands can beplaced within 20 MHz.

As will be described later, the cell searching apparatus of the mobilestation only filters the synchronization channel occupied band 200 sothat the performance of the cell searching process can be improved.

The base station of the present invention transmits the primarysynchronization channel, secondary synchronization channel, common pilotchannel, and data channel to the mobile station in the cell.

FIG. 19 is a block diagram of the base station according to anembodiment of the present invention. The base station includes asynchronization channel generator 400, a common pilot channel generator401, a traffic channel generator 402, a diversity controller 403, OFDMsymbol mapping units 404-A and 404-B, scramblers 405-A and 405-B,Inverse Fast Fourier Transformers (IFFT) 406-A and 406-B, prefix insertunits 407-A and 407-B, IF/RF units 408-A and 408-B, and transmittingantennas 409-A and 409-B.

The traffic channel generator 402 generates traffic data to betransmitted as in reference numeral 220 of FIGS. 9, 11, and 17, and thecommon pilot channel generator 401 generates the pilot symbol defined inreference numeral 210 of FIGS. 9, 11, and 17. Also, the synchronizationchannel generator 400 generates the primary synchronization channelsymbol and the secondary synchronization channel symbol.

The OFDM symbol mapping units 404-A and 404-B map symbol values of eachchannel to positions on the frequency domain as in FIG. 9, 11, or 17.The scramblers 405-A and 405-B multiply scrambling codes that are uniqueto each base station on the frequency domain with respect to an outputof the OFDM symbol mapping units 404-A and 404-B, that is, the OFDMsymbols, in addition to the synchronization channel symbols among themapping results.

The IFFT 406-A and 406-B inverse fourier transform an output of thescramblers 405-A and 405-B to generate the time domain signal.

The prefix insert units 407-A and 407-B insert cyclic prefix CP whichcan demodulate an OFDM signal even in multipath delay of the channelinto the output of the IFFT 406-A and 406-B.

In the current base station, when the primary synchronization channeland the secondary synchronization channel defined in FIG. 16 are formedby the TDM method, the primary synchronization channel is placed at theend of the sub-frame, and the secondary synchronization channel isplaced at the front of the next sub-frame, the prefix insert units 407-Aand 407-B insert the CP as well as the postfix 390 into the output ofthe IFFT 406-A and 406-B as in FIG. 16B or 16D with respect to thesymbols placed in the secondary synchronization channel, when thecurrent sub-frame has long CP.

The IF/RF units 408-A and 408-B up-convert a signal output from theprefix insert units 407-A and 407-B, that is a baseband signal, into aband pass signal and amplify the up-converted signal.

The transmitting antennas 409-A and 409-B transmit the amplified signal.

In FIG. 19, there are two transmitting antennas 409-A and 409-B. Thatis, when the base station according to an embodiment of the presentinvention includes only one transmitting antenna 409-A without thetransmitting antenna 409-B, the OFDM symbol mapping unit 404-B, thescrambler 405-B, the IFFT 406-B, the prefix insert unit 407-B, the IF/RFunit 408-B, and the diversity controller 403 can be excluded.

In FIG. 19, the synchronization channel symbol is transmitted to atransmitting end of the base station system which has transmittingdiversity by using two transmitting antennas.

The transmitting diversity controlled by the diversity controller 403illustrated in FIG. 19 is now described. In order to obtain spacediversity, synchronization channel symbols included in adjacent syncblocks 140 are respectively transmitted to each different antenna inFIG. 8.

For example, the synchronization channel symbol included in the firstsync block is transmitted to the first transmitting antenna 409-A, thesynchronization channel symbol included in the second sync block istransmitted to the second transmitting antenna 409-B, synchronizationchannel symbol included in the third sync block is transmitted again tothe first transmitting antenna 409-A.

The diversity controller 403 performs switching in order to perform thediversity described above. That is, a Time Switching Transmit Diversity(TSTD) is applied to the synchronization channel. The diversitycontroller 403 switches the output of the synchronization channelgenerator and provides the switched output to the OFDM symbol mappingunit 404-A or the OFDM symbol mapping unit 404-B.

The TSTD is applied to the TDM method in FIG. 10 or FIG. 14, however,the primary synchronization channel symbol and the secondarysynchronization channel symbol that are adjacent to each other should betransmitted to the same antenna so that the mobile station cancoherently demodulate the secondary synchronization channel symbol byusing the channel estimation value of the primary synchronizationchannel symbol.

Meanwhile, in addition to the space diversity or TSTD diversity, a delaydiversity can be applied as the transmitting diversity.

FIG. 20 is a block diagram of a receiver of the mobile station accordingto an embodiment of the present invention. The mobile station includesat least one receiving antenna. In FIG. 20, there are two receivingantennas.

Referring to FIG. 20, the receiver of the mobile station includesreceiving antennas 500-A and 500-B, down converter 510-A and 510-B, acell searching unit 600, a data channel demodulator 520, a controller530, a clock generator 540.

The RF signal formed frames transmitted from each base station arereceived through the receiving antennas 500-A and 500-B and areconverted into baseband signals S1 and S2 through the down converter510-A and 510-B.

The cell searching unit 600 searches for target cell by using theprimary synchronization channel symbol and the secondary synchronizationchannel symbol included in the baseband signals S1 and S2 that are downconverted, and the common pilot channel symbol.

Examples of the cell searching result include detecting thesynchronization channel symbol of the target cell, sync block timing,frame boundary, and cell identifiers. Examples of target cell searchinginclude searching for an initial cell by the mobile station andsearching for an adjacent cell for handover.

The controller 530 controls the cell searching unit 600 and the datachannel demodulator 520. That is, the controller 530 controls the cellsearching unit 600 and then controls timing and invert scrambling of thedata channel demodulator 520 based on the result of the cell searching.

The data channel demodulator 520 demodulates traffic channel data asillustrated in reference numeral 220 of FIGS. 9, 11, and 17 included inthe down converted signals according to the control by the controller530. Meanwhile, all hardware of the mobile station is synchronized withclocks generated by the clock generator 540 and is operated.

Referring FIG. 20, the cell searching apparatus 600 includessynchronization channel band filters 610-A and 610-B, a synchronizationand group detecting unit 620, a hopping code detecting unit 640, and acell identifier detecting unit 680.

The synchronization channel band filters 610-A and 610-B perform a bandpass filtering for only synchronization channel occupied band 200 to bepassed from among a whole OFDM signal band 310 with respect to the downconverted signals S1 and S2, as illustrated in FIGS. 9, 11, and 17.

The synchronization and group detecting unit 620 obtains synchronizationinformation (that is, synchronization channel symbol timing, sync blocktiming, or sync block boundary) S5 and cell group information (primarysynchronization channel sequence number) S6 by using a primarysynchronization channel signal included in the filtered signal S3 andS4.

The hopping code detecting unit 640 detects cell sub-group identifiersS7 and timing (boundary) information of the frame S8 by using thesynchronization information S5, cell group information (primarysynchronization channel sequence number) S6, and the hopping code wordtable as in Table 1 previously stored in the memory of the mobilestation and transmits the detected results to the cell identifierdetecting unit 680.

Here, coherent demodulation based on the channel estimation obtained byusing the primary synchronization channel code that is obtained from theprevious process is performed so that the performance of the second cellsearching process can be improved.

When the cellular system uses the third, fourth, or sixth method ofallocating a code respectively illustrated in FIGS. 3, 4, and 5B, thesub-groups are one-to-one mapped to the cell identifiers so that thesub-group identifiers becomes the cell identifiers as they are.

The role of the hopping code detecting unit 640 according to the methodof allocating a code of the present invention is now described.

In the first method of allocating a code, the hopping code detectingunit 640 uses synchronization and the cell group information (primarysynchronization channel sequence number) obtained from thesynchronization and group detecting unit 620 and detects the cyclicshifted hopping code words of the target cell by using the secondarysynchronization channel signal included in the filtered signals S3 andS4. Then, the hopping code detecting unit 540 detects the cell sub-groupidentifiers S7 and timing (boundary) information of the frame S8 of thetarget cell which correspond to the cyclic shifted hopping code wordsand transmits them to the cell identifier detecting unit 680.

In the second method of allocating a code, the hopping code detectingunit 640 uses synchronization information obtained from thesynchronization and group detecting unit 620 and detects the cyclicshifted hopping code words of the target cell by using the secondarysynchronization channel signal included in the filtered signals S3 andS4. Then, the hopping code detecting unit 540 detects the cell sub-groupidentifiers S7 and timing (boundary) information of the frame S8 of thetarget cell by using the cyclic shifted hopping code words and the cellgroup information (primary synchronization channel sequence number) andtransmits them to the cell identifier detecting unit 680.

In the third method of allocating a code, the hopping code detectingunit 640 uses synchronization and cell group information (primarysynchronization channel sequence number) obtained from thesynchronization and group detecting unit 620 and detects the cyclicshifted hopping code words of the target cell by using the secondarysynchronization channel signal included in the filtered signals S3 andS4. Then, the hopping code detecting unit 640 detects the cell sub-groupidentifiers S7 and timing (boundary) information of the frame S8 of thetarget cell which correspond to the cyclic shifted hopping code wordsand transmits them to the cell identifier detecting unit 680. In thiscase, since the cell sub-group identifiers are one-to-one mapped to thecell identifiers, the cell sub-group identifiers S7 are the same as cellidentifiers S9 so that the cell identifier detecting unit 680 isoperated to a confirmation mode for the previous process or can bebypassed.

In the fourth method of allocating a code, the hopping code detectingunit 640 uses the synchronization information obtained from thesynchronization and group detecting unit 620 and detects the cyclicshifted hopping code words of the target cell by using the secondarysynchronization channel signal included in the filtered signals S3 andS4. Then, the hopping code detecting unit 640 detects the cell sub-groupidentifiers S7 and timing (boundary) information of the frame S8 of thetarget cell by using the cyclic shifted hopping code words and the cellgroup information (primary synchronization channel sequence number)obtained from the synchronization and group detecting unit 620 andtransmits them to the cell identifier detecting unit 680. In this case,since the cell sub-group identifiers are one-to-one mapped to the cellidentifiers, the cell sub-group identifiers S7 are the same as the cellidentifiers S9 so that the cell identifier detecting unit 680 isoperated to a confirmation mode for the previous process or can bebypassed.

In the fifth method of allocating a code, the hopping code detectingunit 640 uses the synchronization information obtained from thesynchronization and group detecting unit 620 and detects the cyclicshifted hopping code words of the target cell by using the secondarysynchronization channel signal included in the filtered signals S3 andS4. Then, the hopping code detecting unit 640 detects the cell sub-groupidentifiers S7 and timing (boundary) information of the frame S8 of thetarget cell which correspond to the cyclic shifted hopping code wordsand transmits them to the cell identifier detecting unit 680.

In the sixth method of allocating a code, the hopping code detectingunit 640 uses the synchronization information obtained from thesynchronization and group detecting unit 620 and detects the cyclicshifted hopping code words of the target cell by using the secondarysynchronization channel signal included in the filtered signals S3 andS4. Then, the hopping code detecting unit 640 detects the cell sub-groupidentifiers S7 and the frame timing (boundary) information S8 of thetarget cell which correspond to the cyclic shifted hopping code wordsand transmits them to the cell identifier detecting unit 680. In thiscase, since the cell sub-group identifiers are one-to-one mapped to thecell identifiers, the cell sub-group identifiers S7 are the same as thecell identifiers S9 so that the cell identifier detecting unit 680 isoperated to a confirmation mode for the previous process or can bebypassed.

In the seventh method of allocating a code, the mobile station cellsearching unit 600 does not include the hopping code detecting unit 640and directly delivers the synchronization information (that is,synchronization channel symbol timing, sync block timing, or sync blockboundary) S5 and the cell group information (the number of primarysynchronization channel sequence) S6 obtained from the synchronizationand group detecting unit 620 to the cell identifier detecting unit 680.

Meanwhile, in the case of the first, second, and fifth methods ofallocating a code, the cell identifier detecting unit 680 receivestiming (boundary) information of the frame S8 and the cell sub-groupidentifiers S7 obtained from the hopping code detecting unit 640 anddetects the cell identifiers through a pilot correlation with respect tothe common pilot channel signal among the down converted signals S1 andS2.

Here, the number of pilot correlations is the same as the number of cellidentifiers in the sub-group received from the hopping code detectingunit and the pilot scrambling codes of each pilot correlator areone-to-one mapped to the cell identifiers.

In the case of the second, third, and sixth methods of allocating acode, since the cell sub-group identifiers S7 received from the hoppingcode detecting unit 640 are one-to-one mapped to the cell identifiers,the cell identifier detecting unit 680 regards the cell sub-groupidentifiers S7 received from the hopping code detecting unit 640 as thecell identifiers S9 and may transmit the cell sub-group identifiers S7to the controller 530.

In the case of the second, third, and sixth methods of allocating acode, since the cell sub-group identifiers S7 received from the hoppingcode detecting unit 640 are one-to-one mapped to the cell identifiers,the cell identifier detecting unit 680 receives the frame timing(boundary) information S8 and the cell sub-group identifiers S7 obtainedfrom the hopping code detecting unit 640 and can be used to verify thecell identifiers through a pilot correlation with respect to the commonpilot channel signal among the down converted signals S1 and S2. Here,the number of pilot correlators is 1 and the pilot scrambling codes ofthe correlator are the codes corresponding to the cell identifiers thatare one-to-one mapped to the cell sub-group identifiers S7.

FIG. 21 is a block diagram of the synchronization and group detectingunit 620 of FIG. 20.

Referring to FIG. 21, the synchronization and group detecting unit 620includes parallel correlators 621-A and 621-B, an accumulator 623, and atiming and cell group determining unit 624.

The parallel correlators 621-A and 621-B previously store the timedomain signals corresponding to the primary synchronization channelsequences available as much as the total number of the cell groups (forexample, 8 in FIG. 1) used in the system and perform a parallelcorrelation to the stored signals with the signals S3 and S4 output fromsynchronization channel band filters 610-A and 610-B.

In addition, when a plurality of the primary synchronization channelsequence is used in the fifth and sixth methods of allocating a code,the time domain signals corresponding to the primary synchronizationchannel sequences are previously stored and a parallel correlation isperformed to the stored signals with the signals S3 and S4 output fromsynchronization channel band filters 610-A and 610-B.

In the case of FIG. 10 or FIG. 14 where the primary synchronizationchannel and the secondary synchronization channel are formed by the TDMmethod, a parallel correlation using the time domain signals of theavailable primary synchronization channel sequences can be performed ora differential correlation using a time domain repeated pattern of theprimary synchronization channel can be performed.

When the differential correlation is performed by using a differentialcorrelator, computation amount is much lower than when the parallelcorrelation using replica of the time domain signals of the primarysynchronization channel sequences is performed by using a parallelcorrelator so that the cell searching apparatus of the mobile stationcan be simplified. In addition, the number of differential correlatorsdoes not relate to the number of cell groups.

On the other hand, the number of parallel correlators corresponds to thenumber of cell groups used in the system, that is, the number of primarysynchronization channel sequences. When the differential correlator isused, the performance thereof may be worse than that of the parallelcorrelator.

Meanwhile, in the FDM method of FIG. 8, the differential correlatorcannot be used. In this specification, the parallel correlator suggestedfrom FIG. 21 is focused.

3840 outputs (samples) are generated per sync block lengths from each ofthe parallel correlators 621-A and 621-B with reference to FIGS. 8, 10,and 14. The timing and cell group determining unit 624 detects thelocation of the sample which generates the peak value from among thedifferential correlation values and determines the same detectedlocation as the synchronization channel symbol timing (in the FDMmethod) or the primary synchronization channel symbol timing (in the TDMmethod).

The synchronization and group detecting unit 620 may further include theaccumulator 623 as in FIG. 21 in order to improve the performance ofdetecting symbol synchronization. The number of samples, that is, 3840,is only an example based on parameters of the OFDM system when thelength of the sync block is the same as 4 sub-frames.

The accumulator 623 firstly combines the outputs from the parallelcorrelators 621-A and 621-B with respect to two receiving antennas andthen adds the antennal combining values with respect to 3840 samplelocations per sync block to each combining value with respect to thesamples that are off by a sync block from each of the sample locations.

When the parallel correlators, which perform a time domain replicacorrelation of the primary synchronization channel, are employed, 3840buffers are needed for the primary synchronization channel signals.

When the synchronization and group detecting unit 620 includes theaccumulator 623, the timing and cell group determining unit 624 detectsthe maximum value from among 3840×N_(G) stored in the accumulator 623(in the case of the parallel correlator, N_(G) is the number of cellgroups) outputs the sample location of the detected maximum value andcorresponding group information as the synchronization information S5and the cell group S6.

FIG. 22 is a graph showing an output from the correlator with respect toN_(G)−1^(th) primary synchronization channel signal from among theoutputs from the parallel correlators 621-A and 621-B of FIG. 21. Forconvenience, it is assumed that the channel between the base stationtransmitting end and the mobile station receiving end is in an idealchannel environment without fading and noise.

FIG. 23 illustrates an input signal provided by the hopping codedetecting unit 640 based on a synchronization channel OFDM symbol timingobtained from the synchronization and group detecting unit 620 in thesystem having the forward link frame structure as in FIG. 8 where theprimary synchronization channel and the secondary synchronizationchannel are formed by the FDM.

Based on the synchronization channel OFDM symbol timing 641 obtained bythe synchronization and group detecting unit 620, cyclic prefixes ofeach OFDM symbol are removed and accordingly N_(S) sample values areinput to the hopping code detecting unit 640 in each sync block.Meanwhile, reference numerals 642-A, 642-B, 642-C, 642-D, and 642-Eindicate the locations of the synchronization channel symbols obtainedby the synchronization channel OFDM symbol timing 641.

FIG. 24 illustrates an input signal provided by the hopping codedetecting unit 640 based on a synchronization channel OFDM symbol timingobtained from the synchronization and group detecting unit 620 in thesystem having the forward link frame structure as in FIG. 10 or FIG. 14where the primary synchronization channel and the secondarysynchronization channel are formed by the TDM.

Based on the synchronization channel OFDM symbol timing 647 obtained bythe synchronization and group detecting unit 620, cyclic prefixes ofeach OFDM symbol are removed and accordingly 2*N_(S) sample valuescorresponding to the primary synchronization channel symbol section andthe secondary synchronization channel symbol section are input to thehopping code detecting unit 640 in each sync block.

Meanwhile, the reference numerals 643-A, 643-B, 643-C, 643-D, and 643-Eindicate the locations of the primary synchronization channel symbolsobtained by the synchronization channel OFDM symbol timing 641 and thereference numerals 644-A, 644-B, 644-C, 644-D, and 644-E indicate thelocations of the secondary synchronization channel symbols.

When the primary synchronization channel is placed at the end of thesub-frame and the secondary synchronization channel is placed at thefirst symbol of the next frame as illustrated in FIGS. 14 and 16, aninterval 646 between a primary synchronization channel symbol section643 and a secondary synchronization channel symbol section 644 of theinput signal provided to the hopping code detecting unit 640 should bethe same as the short CP at all times.

FIG. 25 is a block diagram of the hopping code detecting unit 640 ofFIG. 20. The hopping code detecting unit 640 includes a frequency offsetdetecting and correcting unit 645 and a sub-group and boundary detectingunit 650.

Firstly, the operation of the frequency offset detecting and correctingunit 645 is described with reference to the cellular system in which theprimary synchronization channel and the secondary synchronizationchannel are formed by the FDM as in FIG. 8.

The frequency offset detecting and correcting unit 645 sets thesynchronization channel OFDM symbol timing 641 based on the output S5synchronization information of the synchronization and group detectingunit 620 and stores P×N_(S) reception signal samples 642-A through 642-Eof the synchronization channel section provided from the synchronizationchannel band filters 610-A and 610-B throughout various sync blocklength sections based on the synchronization channel OFDM symbol timing641. Then, the frequency offset detecting and correcting unit 645estimates frequency offset by using the samples and a replica of theprimary synchronization channel signal corresponding to the cell groupS6 received from the synchronization and group detecting unit 620 andcorrects frequency offset with respect to P×N_(S) reception signalsamples 642-A through 642-E based on the estimated frequency offset S10,thereby providing P×N_(s) corrected reception signal samples S11 and S12to the sub-group and boundary detector 650.

Here, P indicates the number of synchronization channel symbols used forfrequency offset correcting, code group detecting, and frame boundarydetecting and may indicate the number of synchronization channel symbolsincluded in one frame. In this case, P=5 with reference to FIG. 8.

A frequency offset estimation method by the frequency offset detectingand correcting unit 645 in the system according to the present inventionwhere the primary synchronization channel and the secondarysynchronization channel are formed by the FDM is represented in Equation3.

$\begin{matrix}{{\Delta \; f} = {\frac{R_{s}}{\pi \; N_{s}}\arg \begin{Bmatrix}{\sum\limits_{a = 0}^{A - 1}{\sum\limits_{p = 0}^{P - 1}\left\{ {\sum\limits_{n = 0}^{\frac{N_{s}}{2} - 1}\left\{ {{r_{a,p}(n)}{S_{g}^{\star}(n)}} \right\}} \right\}^{\star}}} \\\left\{ {\sum\limits_{n = \frac{N_{s}}{2}}^{N_{s} - 1}\left\{ {{r_{a,p}(n)}{S_{g}^{\star}(n)}} \right\}} \right\}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, R_(S) is an OFDM sampling frequency, A is the number of receivingantennas, and P is the number of synchronization channel symbols used toestimate frequency offset.

In addition, r_(a,p)(n) indicates n^(th) sample value from among N_(S)samples of P^(th) synchronization channel symbol from thesynchronization channel OFDM symbol timing 641 provided from thesynchronization and group detecting unit 620 with respect to a^(th)receiving antenna.

Sg(n) indicates the time domain signal (replica) of the primarysynchronization channel which corresponds to cell group number g. * is acomplex conjugate.

In the case of the cellular system where the primary synchronizationchannel and the secondary synchronization channel are formed by the TDMas in forward link frame of FIG. 10 or FIG. 14, the operation of thefrequency offset detecting and correcting unit 645 is as follows.

The frequency offset detecting and correcting unit 645 sets the firstsynchronization channel OFDM symbol timing 647 based on the output S5synchronization information of the synchronization and group detectingunit 620 and stores P×N_(s) reception signal samples 643-A through 643-Eof the primary synchronization channel section provided from thesynchronization channel band filters 610-A and 610-B throughout varioussync block length sections based on the first synchronization channelOFDM symbol timing 647. Then, the frequency offset detecting andcorrecting unit 645 estimates frequency offset by using the samples andcorrects frequency offset with respect to P×N_(S) reception signalsamples 643-A through 643-E of the primary synchronization channelsection and P×N_(S) reception signal samples 644-A through 644-E of thesecondary synchronization channel section, based on the estimatedfrequency offset S10, thereby providing P×N_(S) corrected receptionsignal samples of the primary synchronization channel section andP×N_(S) corrected reception signal samples of the secondarysynchronization channel section S11 and S12 to the sub-group andboundary detector 650.

As will be described later, the samples 643-A through 643-E of theprimary synchronization channel are used for channel estimation whilethe secondary synchronization channel is coherently demodulated.

Here, P indicates the number of synchronization channel symbols used forfrequency offset correcting, code group detecting, and frame boundarydetecting and may indicate the number of synchronization channel symbolsincluded in one frame. In this case, P=5 with reference to FIGS. 10 and14.

A frequency offset estimation method by the frequency offset detectingand correcting unit 645 in the system according to the present inventionwhere the primary synchronization channel and the secondarysynchronization channel are formed by the TDM is represented in Equation4. In the TDM method, since the reception signals 644-A through 644-E inthe primary synchronization channel section have a characteristic ofrepetition on the time axis, a differential correlation can be used asin Equation 4.

$\begin{matrix}{{\Delta \; f} = {\frac{R_{s}}{\pi \; N_{s}}{t{an}}^{- 1}\begin{Bmatrix}{\sum\limits_{a = 0}^{A}{\sum\limits_{p = 0}^{P - 1}\sum\limits_{n = 0}^{\frac{N_{s}}{2}}}} \\\left\{ {{r_{a,p}^{\star}(n)}{r_{a,p}\left( {n + \frac{N_{s}}{2}} \right)}} \right\}\end{Bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Here, R_(S) is an OFDM sampling frequency, A is the number of receivingantennas, and P is the number of synchronization channel symbols used toestimate frequency offset.

In addition, r_(a,p)(n) indicates n^(th) sample value from among N_(S)samples of P^(th) synchronization channel symbol from thesynchronization channel OFDM symbol timing 647 provided from thesynchronization and group detecting unit 620 with respect to a^(th)receiving antenna.

Meanwhile, Equation 5 represents frequency offset estimation method bythe frequency offset detecting and correcting unit 645.

$\begin{matrix}{{{r_{a,p}^{\prime}(n)} = {{r_{a,p}(n)} \times \exp \left\{ {{- j}\; 2\pi \frac{\Delta \; f}{R_{s}}n} \right\}}},{n = 0},1,2,\ldots \mspace{14mu},{N_{s} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

That is, the frequency offset detecting and correcting unit 645 correctsP×N_(S) reception signal samples of FIG. 23 by using the frequencyoffset value estimated by the method above or corrects frequency offsetsof 2×P×N_(S) reception signal samples of FIG. 24 by using Equation 4.The frequency offset detecting and correcting unit 645 providescorrected frequency offset samples r′_(a,p) (S11 and S12) to thesub-group and boundary detector 650 sequentially by N_(S).

The sub-group and boundary detector 650 detects the sub-groupidentifiers and 10 msec frame timing by using the corrected frequencyoffset samples S11 and S12 and the hopping codes as in FIG. 1 which arepreviously stored and provides the detected cell sub-group identifiersS7 and the frame timing (boundary) information S8 to the cell identifierdetecting unit 680.

FIG. 26 is a block diagram of the sub-group and boundary detector 650 ofFIG. 25. The sub-group and boundary detector 650 includes codecorrelation calculating units 665-A and 665-B, a combiner 656, acorrelation buffer 657, a hopping code storing unit 659, a code worddetecting unit 658, a boundary detecting unit 649, and a sub-groupdetecting unit 648.

Since the synchronization channel sequence index included in each of thesecondary synchronization channel symbols are unknown, the mobilestation should calculate all possible sequences with respect to N_(S)samples of the synchronization channel symbols.

The code correlation calculating units 665-A and 665-B calculatecorrelation for each of the secondary synchronization channel sequencesused in the system with respect to the secondary synchronization channelsymbols S11 and S12 in which frequency offset is corrected from thefrequency offset detecting and correcting unit 645.

The combiner 656 combines the outputs of the code correlationcalculating units 665-A and 665-B and provides N−1 combined correlationvalues to each synchronization channel symbol.

The correlation buffer 657 buffers N−1 correlation values with respectto the secondary synchronization channel symbols as much as the numberof estimation P. Ultimately, P×(N−1) correlation values are stored inthe correlation buffer 657.

The hopping code storing unit 659 stores a plurality of the hopping codewords as in Table 1.

The code word detecting unit 658 calculates the total sum of thecorrelation values of the synchronization channel sequences that aremapped to each of the hopping code word element index with respect tothe stored hopping code words and all the cyclic shifted code words ofthe stored hopping code words and detects cyclic shifted hopping codeword numbers implied to the synchronization channel symbols based on thecalculated result.

The boundary detecting unit 649 detects the frame timing (boundary)information S8 based on the cyclic shift index with respect to thedetected hopping code words. In addition, the sub-group detecting unit648 detects the cell sub-group identifiers S7 based on the detectedhopping code word numbers. The detailed detecting processes aredescribed later.

In particular, when the synchronization channel sequence is based on theGCL sequence, the code correlation calculating units 665-A and 665-Bincludes first data obtaining units 800-A and 800-B, second datagenerating units 653-A and 653-B, and correlation generating units 820-Aand 820-B with reference to FIG. 26. The code correlation calculatingunits 665-A and 665-B in FIG. 26 use a non-coherent method which onlyuses the secondary synchronization channel symbols. In the case of thecoherent method, the channel estimation values estimated by using theprimary synchronization channel can be used in demodulating thesecondary synchronization channel.

In this specification, the non-coherent method will be focused anddescribed.

Referring to FIG. 26, the first data obtaining units 800-A and 800-Binclude Fourier converters 651-A and 651-B and demappers 652-A and652-B. The Fourier converters 651-A and 651-B Fourier convert thesamples S11 and S11 for the secondary synchronization channel symbolsection to obtain N_(S) frequency domain values and the demappers 652-Aand 652-B obtain data of the subcarrier to which the chips of thesecondary synchronization channel sequence are allocated from among theobtained N_(S) frequency domain values.

The second data generating units 653-A and 653-B are provided outputsfrom the demappers 652-A and 652-B and perform differential encodingdefined as Equation 6.

u(n)=y*(n)y((n−1)_(mod N)), n=0,1, . . . , N−1  [Equation 6]

Here, y(n) is the output of the demappers 652-A and 652-B and u(n) isthe output of the second data generating units 653-A and 653-B. Thedifferential encoding is performed to obtain only linear phase shiftthat corresponds to GCL sequence number k in N frequency domain signalcomponent. That is, when it is assumed that channel distortion and noisedo not exist, u(n) is represented as Equation 7.

$\begin{matrix}{{{u(n)} = {\exp \left\{ {{- j}\; 2\; \pi \frac{n}{N}k} \right\}}},\mspace{14mu} {n = 0},1,\ldots \mspace{14mu},{N - 1}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

K is a GCL sequence identifier and may have values of 1 to N−1 assuggested in Equation 1.

The correlation generating unit 820-A and 820-B inverse-fourier convertN u(n) of the synchronization channel symbols, that is, the output ofthe second data generating units 653-A and 653-B, and calculatecorrelation of the synchronization channel symbols with respect to eachhopping code word by using an absolute value of the conversion result(the non-coherent method). Referring to FIG. 26, the correlationgenerating unit 820-A and 820-B include inverse Fourier converters 654-Aand 654-B and size calculating units 655-A and 655-B.

The inverse Fourier converters 654-A and 654-B inverse-fourier convertthe output of the second data generating units 653-A and 653-B andgenerate N complex samples per each synchronization channel symbol. Thesize calculating units 655-A and 655-B add the square of a realcomponent with the square of an imaginary component with respect to Ngenerated complex samples and calculate the size of the complex samples.

In particular, the first vale among the calculated N values is removedand only remaining N−1 values are provided to the combiner 656.

FIG. 27 is a graph showing the outputs of the code correlationcalculating units 665-A and 665-B of FIG. 26.

A horizontal axis shows the secondary synchronization channel sequence(GCL sequence) numbers and a vertical axis shows correlation valuesbetween the current received secondary synchronization channel symbol(that is, N−1) and the synchronization channel sequence (GCL sequence).

In particular, FIG. 27 shows the outputs of the code correlationcalculating units 665-A and 665-B when the hopping code word elementindex k included in the currently received secondary synchronizationchannel symbol is 2.

Referring to FIG. 27, a correlation value when k is 2 is the largest. Inparticular, when there is no channel distortion or noise, correlationvalues at remaining hopping code index, except for when k is 2, are “0”,as differently in FIG. 27.

In FIG. 27, a receiving diversity is applied to the mobile station byinstalling two receiving antennas. The combiner 656 combines the outputsof the code correlation calculating units 655-A and 655-B obtained byeach path according to the receiving diversity. When the receivingdiversity is not used, the combiner 656 and the code correlationcalculating unit 665-B can be excluded.

The hopping code word identifiers are one-to-one mapped to the sub-groupidentifiers of FIG. 2 and the cyclic shift index indicates how far 10msec frame boundary is off from the point (641 or 647) used in thehopping code detecting unit 640.

Ultimately, 10 msec frame boundary can be obtained from thesynchronization information 641 or 647 obtained from the first cellsearching process and the cyclic shift index.

FIG. 28 illustrates P×(N−1) correlation values stored in the correlationbuffer 657 of FIG. 26. Here, P is 5 and N is 41. A horizontal axis showsthe secondary synchronization channel sequence numbers and a verticalaxis shows correlation values of each of the synchronization channelsequences with respect to the received synchronization channel symbols.

The reference numeral 662-A shows a correlation of 40 synchronizationchannel sequences with respect to when the first synchronization channelsymbol, that is, when p=0. The reference numerals 662-B, 662-C, 662-D,and 662-E are 40 correlation values calculated with respect to thereceived synchronization channel symbols respectively corresponding top=1, 2, 3, and 4.

That is, the top 40 samples 662-A are the outputs of the combiner 656with respect to the first OFDM symbol 642-A in FIG. 23 or the firstsecondary synchronization channel symbol 644-A in FIG. 24.

The second 40 samples 662-B are the outputs of the combiner 656 withrespect to the second OFDM symbols 642-B and 644-B. The third 40 samples662-C are the outputs of the combiner 656 with respect to the third OFDMsymbols 642-C and 644-C. The fourth 40 samples 662-D and the fifth 40samples 662-E are same as above.

The code word detecting unit 658 calculates N_(H)×P decision variablesand selects the decision variable having the maximum value from amongthe decision variables. Then, the code word detecting unit 658 providesinformation on the selected decision variable to the boundary detectingunit 649 and the sub-group detecting unit 648. Here, N_(H) is the numberof hopping code words included in one cell group. In the first throughfourth methods of allocating a code in FIGS. 1 through 4, N_(H) is 16and in the fifth and sixth methods of allocating a code in FIGS. 5A and5B, N_(H) is 128.

That is, the code word detecting unit 658 performs a test only for N_(H)hopping code words included in the cell group information S6 receivedfrom the synchronization and group detecting unit 620.

For example, when it is assumed that the mobile station is included inthe cellular system in which the first method of allocating a code inFIG. 1 is used, when the synchronization and group detecting unit 620detects the cell group identifier 2 in the first cell searching process,the code word detecting unit 658 performs a hypothesis test only for thehopping code words included in the cell group 2, that is, the hoppingcode words with identifiers 32, 33, 34, . . . , 45, 46, 47.

The boundary detecting unit 649 and the sub-group detecting unit 648respectively detect the cell sub-group identifiers S7 and timing(boundary) information of the frame S8 based on the results of thehypothesis test.

When the first, third, fifth, or sixth method of allocating a coderespectively in FIG. 1, FIG. 3, FIG. 5A, and FIG. 5B is used in thecellular system, the decision variable w(i) for the hypothesis test tobe performed by the code word detecting unit 658 is represented asEquation 8.

$\begin{matrix}{{{w(i)} = {\sum\limits_{u = 0}^{P - 1}{v_{u}\left( {h_{\lfloor{i/P}\rfloor}\left( \left( {i_{{mod}\; P} + u} \right)_{{mod}\; P} \right)} \right)}}}{{i = {k_{g} \times P \times N_{H}}},{{k_{g} \times P \times N_{H}} + 1},\ldots \mspace{14mu},\left( {k_{g} + 1} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Here, mod is a modular operator and [x] is the maximum value from amongpositive numbers that are same or less than x. k_(g) is the cell groupnumber 10 and N_(H) is the number of hopping code words in the cellgroup.

In addition, P is the length of the hopping code word or the number ofsynchronization channel symbols per 10 msec frame and P is 5 accordingto FIG. 1 and Table 1. h_(x)(y) is y^(th) element index of the hoppingcode word that is index x. For example, when x=0 and y=2, h₀(2) is 6with reference to Table 1.

In Equation 8, v_(u)(k) is a correlation value of the synchronizationchannel sequence which is index k with respect to index k located onu^(th) OFDM symbol and is stored in the correlation buffer 657.

Equation 8 represents decision variables with respect to the hoppingcode words corresponding to the cell group numbers from among thehopping codes of Table 1 and their cyclic shifted code words.

That is, the decision variable with respect to the hopping code word 4,5, 6, 7, 8 of index 0 is w(0), the decision variable with respect to the“1” cyclic shifted code words 8, 4, 5, 6, 7 of the hopping code words ofindex 0 is w(1), and the decision variable of “u” cyclic shifted codewords of the hopping code words of index i is w(i×P+u).

The process of calculating w(i) will be described more fully withreference to FIG. 28 and Table 1. Firstly, it is assumed that the firstmethod of allocating a code (refer to FIG. 1) is applied to the cellularsystem. When the cell group number detected by the synchronization andgroup detecting unit 620 is 0 in the first cell searching process, thecode word detecting unit 658 calculates the decision variables, that is,w(0), w(1), . . . , w(5*16-1), with respect to 16 hopping code wordscorresponding to cell group number 0 and their cyclic shifted codewords.

Since w(0) is the decision variable with respect to the code words 4, 5,6, 7, 8 in which the cyclic shift index is 0 and the identifier of thehopping code word is 0, w(0)=0.9+1.9+1.6+1.7+1.7=7.8. Since w(2) is thedecision variable with respect to the code words 7, 8, 4, 5, 6 in whichcyclic shift index is 2 and the identifier of the hopping code word is0, w(2)=10.2+8.3+9.4+9.1+8.9=45.9.

After such process, w(0), w(1), . . . , w(5×16-1) are calculated. Whenw(2) has the largest value, the code word detecting unit 658 finallydetermines that identifier is 0 and the cyclic shift index is 2.According to the determination result, the frame boundary and the codegroup are detected.

That is, when index of the decision variable having the largest valuefrom among P×N_(H) decision variables w(k_(g)×N_(H)*P),w(k_(g)×N_(H)*P+1), . . . , w((k_(g)+1)×N_(H)×P−1) is i_(max), that is

${i_{\max} = {\begin{matrix}\max \\i\end{matrix}{w(i)}}},$

the code word detecting unit 658 calculates index of the hopping codeword and the cyclic shift index as [i_(max)÷P], (i_(max))_(mod P). Sincethe hopping code words are one-to-one mapped to the cell sub-groups, thecell sub-groups are detected from the index of the hopping code wordsand the frame boundary is detected from the cyclic shift index.

According to an embodiment of the present invention, information on thedecision variables provided to the boundary detecting unit 649 and thesub-group detecting unit 648 by the code word detecting unit 658 isi_(max). The boundary detecting unit 649 performs a modular operation(i_(max))_(mod P) to i_(max) provided to detect the cyclic shift indexand detects the frame boundary based on the detected cyclic shift index.

The sub-group detecting unit 648 performs an operation [i_(max)÷P] toi_(max) provided to obtain the index of the hopping code words anddetects the cell sub-group corresponding to the obtained hopping codeword index.

As described above, when each cell sub-group includes only onescrambling code, the hopping code words are one-to-one mapped to thecell identifiers so that the code word detecting unit 658 can detect thescrambling code from the detected sub-group.

Therefore, in this case, the third cell searching process can be omittedor can be used only for verifying the scrambling code detected from thesecond cell searching process.

When the cellular system uses the second or fourth method of allocatinga code in FIG. 2 or FIG. 4, the decision variable for the hypothesistest to be performed by the code word detecting unit 658 is representedas Equation 9.

$\begin{matrix}{{{w(i)} = {\sum\limits_{u = 0}^{P - 1}{v_{u}\left( {h_{\lfloor{i/P}\rfloor}\left( \left( {i_{{mod}\; P} + u} \right)_{{mod}\; P} \right)} \right)}}}{{i = 0},1,\ldots \mspace{14mu},{{P \times N_{H}} - 1}}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

The difference between Equation 9 and Equation 8 is that the hoppingcode words included in each cell sub-group are different by the cellgroups in Equation 8, whereas the hopping code words that are same bythe cell groups are used in Equation 9.

Accordingly, in the case of the second or fourth method of allocating acode in FIG. 2 or FIG. 4, the cell sub-group numbers can be obtained byusing the value obtained by an operation [i_(max)÷P] of the maximumvalue from among the decision variables defined as in Equation 9 fromthe sub-group detecting unit 648 and the cell group information S6received from the synchronization and group detecting unit.

On the other hand, the 10 msec frame boundary is obtained by using thecyclic shift value obtained through the operation (i_(max))_(mod P) asdescribed above.

Meanwhile, the cell identifier detecting unit 680 detects the cellidentifiers based on the frame information obtained in the second cellsearching process. That is, the cell identifier detecting unit 680 canobtain the locations of the common pilot channel symbols, that is, thecommon pilot channel symbol section, based on the detected frameboundary and finally detects the cell identifiers of the target cellthrough a pilot correlation between the common pilot channel symbol andthe scrambling codes that correspond to available cell identifiersincluded in the sub-group detected in the second cell searching processbased on the obtained location.

Meanwhile, similarly to other OFDM symbols, each common pilot channelsymbol is formed of NT samples and includes a cyclic prefix section thatis N_(CP) samples and the remaining section that is N_(S) samples.

In other words, the cell identifier detecting unit 680 extracts thecommon pilot channel symbol included in the received sub-frame based onthe frame timing (boundary) information obtained in the second cellsearching process, calculates the correlation values between theextracted common pilot channel symbol and the scrambling codes includedin the sub-codes detected in the second cell searching process, anddetermines the scrambling code that corresponds to the correlation valuehaving the largest value as the scrambling code of the current basestation.

That is, the common pilot channel is used to estimate channels forcoherently demodulating the forward link data channel and to detect thescrambling code (the scrambling codes are one-to-one mapped to the cellidentifiers) in the third cell searching process.

The cell identifier detecting unit 680 searches only for the scramblingcodes included in the sub-group provided by the code word detecting unit658 so that complexity of the receiver can be reduced. That is, only NCscrambling codes included in the sub-group detected in the second cellsearching process from the cell group detected in the first cellsearching process are searched. Here, N_(c) is the number of scramblingcodes per sub-group and N_(c)=4 in FIG. 1.

FIG. 29 is a block diagram of the cell identifier detecting unit 680 ofFIG. 20. The cell identifier detecting unit 680 includes frequencyoffset correctors 681-A and 681-B, Fourier converters 682-A and 682-B,pilot symbol extractors 683-A and 683-B, pilot correlators 684-A and684-B, sub-frame accumulators 686-A and 686-B, receiving antennacombiners 687, and a peak detector 688.

Since the common pilot channel symbol section by sub-frames can be knownbased on 10 msec timing (boundary) information of the frame S8 providedfrom the hopping code detecting unit 640, the frequency offsetcorrectors 681-A and 681-B correct frequency offset of N_(S) samples,except for cyclic prefix, with respect to the common pilot channelsymbols included in the down-converted OFDM symbols S1 and S2 by usingEquation 6. Here, the frequency offset estimation values used to correctfrequency offset can be the frequency offset estimation value S10provided from the hopping code detecting unit 640.

The Fourier converters 682-A and 682-B Fourier convert N_(S) frequencyoffset corrected samples and generates a frequency domain signal.

The pilot symbol extractors 683-A and 683-B only extract N_(p) pilotdata from the generated frequency domain signal.

The pilot correlators 684-A and 684-B calculate the correlation of theextracted N_(p) pilot data with the N_(c) scrambling codes included inthe code group provided from the hopping code detecting unit 640.

Here, the correlation can be calculated by using Equations 9 through 12.Referring to FIG. 29, the pilot correlators 684-A and 684-B include Ncfrequency domain differential correlators and perform a frequency domaindifferential correlation in a parallel method.

That is, each of the frequency domain differential correlatorscalculates correlation between the scrambling codes included in thedetected code group and the extracted pilot data. The frequency domaindifferential correlator is operated in the common pilot channel symbolsection in each sub-frame and outputs of the frequency domaindifferential correlator are accumulated in each sub-frame accumulatorincluded in the accumulators 686-A and 686-B by Nc scrambling codes inthe detected code group. Equations 9 through 12 will be described later.

The accumulators 686-A and 686-B accumulate Nc correlation valuescalculated with respect to each common pilot channel symbol. Referringto FIG. 8, 10, or 14, at least one common pilot channel symbol existsper sub-frame so that correlation value calculated with respect tocommon pilot channel symbols are accumulated as much as the number ofpreviously set sub-frames. Each of the accumulators 686-A and 686-Bincludes N_(c)sub-frame accumulators.

The combiner 687 combines the outputs of the accumulators 686-A and686-B calculated according to a plurality of paths obtained by thereceiving diversity that is embodied by installing a plurality of thereceiving antennas and generates N_(c) decision variable. Meanwhile, itis well known to one of ordinary skill in the art that the combiner 687and blocks in the lower part can be excluded when the receivingdiversity is not used.

The peak detector 688 detects the decision variable having the largestvalue from among N_(c) decision variables provided from the combiner687, selects the scrambling code corresponding to the detected decisionvariable, and finally detects the scrambling code of the current basestation or the cell identifiers S9. Accordingly, the mobile station candetect the base station having the shortest radio distance or thescrambling code (cell identifier) of the base station having thestrongest reception signal.

Meanwhile, when the largest value detected is larger than the pre-setthreshold, it is regarded that the cell searching is completed and whenthe largest value detected is smaller than the pre-set threshold, thecell searching apparatus repeatedly performs the first, second, andthird cell searching processes.

When each sub-group includes one cell identifier or scrambling code,that is, when Nc is 1, the sub-group identifiers are one-to-one mappedto the cell identifiers so that the frame boundary and the cellidentifiers can be detected even by performing up to the second cellsearching process. Accordingly, the third cell searching process can beexcluded. However, when the third cell searching process is performed,the cell identifiers detected according to the second cell searchingprocess are verified.

Hereinafter, the operation of the pilot correlators 684-A and 684-B willbe described more fully.

FIG. 30 illustrates the operations of the pilot correlators 684-A and684-B according to an embodiment of the present invention.

Reference numerals 695 and 696 respectively illustrate input and outputof the pilot symbol extractors 683-A and 683-B. That is, a signal in thefrequency domain 695, the pilot data and traffic data may co-exist andthe pilot symbol extractors 683-A and 683-B extract Np pilot data.

X(n) in FIG. 30 indicates n^(th) pilot data from among frequency domaindata of the common pilot channel symbol. In particular, the common pilotchannel symbol includes Np pilot data in FIG. 30.

The correlation between extracted pilot data and the scrambling codes isrepresented as Equations 10 through 13.

$\begin{matrix}{\sum\limits_{i = 0}^{\frac{N_{p}}{4} - 1}\begin{Bmatrix}\begin{matrix}\left( {{X\left( {4\; i} \right)}\left( {c_{g_{k}}\left( {4i} \right)} \right)^{\star}} \right) \\{\left( {X\left( {{4i} + 2} \right)\left( {c_{g_{k}}\left( {{4i} + 2} \right)} \right)^{\star}} \right)^{\star} +}\end{matrix} \\\begin{matrix}\left( {{X\left( {{4i} + 1} \right)}\left( {c_{g_{k}}\left( {{4i} + 1} \right)} \right)^{\star}} \right) \\\left( {{X\left( {{4i} + 3} \right)}\left( {c_{g_{k}}\left( {{4i} + 3} \right)} \right)^{\star}} \right)^{\star}\end{matrix}\end{Bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

N_(p) is the number of pilot data on the frequency domain included inthe common pilot channel symbol and c_(gk)(u) is u^(th) element ofk^(th) scrambling code among the scrambling codes included in thedetected code group.

The differential correlation represented as Equation is used in thethird cell searching process according to the following reason. In thecase of the OFDM signal, the adjacent symbols in the frequency domainexperience almost same wireless fading which is similar with channeldistortion experienced by the adjacent symbols. However, in the wirelessfading experienced by the symbols located far from each other, the morethe gap between the symbols increase, the more the independent fading toeach other is experienced. In this case, when the correlation length Nis large, the performance of the existing frequency domain correlatordefined as in Equation 13 is significantly decreased.

$\begin{matrix}{\sum\limits_{i = 0}^{N - 1}\left\{ \left( {{X(i)}\left( {c(i)} \right)^{\star}} \right) \right\}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

$\sum\limits_{i = 0}^{N - 1}\alpha_{i}$

In Equation 11, since X(i)=α_(i)c(i), is coherently added to theindependent symbols X( ) that are far from each other and, as a result,the performance is significantly decreased in a fading channel. α_(i)indicates the channel value of i^(th) subcarrier and is almost same foradjacent subcarriers in the fading channel, however, is different forthe subcarriers that are far from each other.

On the other hand, when the differential correlator defined in Equation12 is used,

$\begin{matrix}{\sum\limits_{i = 0}^{\frac{N}{2} - 1}\left\{ {\left( {{X\left( {2i} \right)}\left( {c\left( {2i} \right)} \right)^{\star}} \right)\left( {{X\left( {{2i} + 1} \right)}\left( {c\left( {{2i} + 1} \right)} \right)^{\star}} \right)^{\star}} \right\}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

the result of the correlation value becomes

${\sum\limits_{i = 0}^{\frac{N}{2} - 1}{\alpha_{2i}\alpha_{{2i} + 1}^{\star}}} \approx {\sum\limits_{i = 0}^{\frac{N}{2} - 1}{\alpha_{2i}}^{2}}$

so that the performance of the differential correlator defined inEquation 12 is better than that of the existing correlator defined inEquation 10.

Instead of using differential multiplication between adjacent symbols asin Equation 10 in the third cell searching process, differentialmultiplication between pilot symbols that are skipped by one step areused as in Equation 10 or reference numeral 697 in FIG. 30, since themobile station cannot identify information of the current base stationwhere the mobile station belongs to in an initial synchronizationobtaining mode. That is, the mobile station cannot identify whether thenumber of transmitting antennas used in the current base station is 1 or2.

When the transmitting antenna is 1, all common pilot channel symbols 696are transmitted through the same transmitting antenna in FIG. 19,however, when the transmitting antenna is 2, even numbered common pilotchannel symbols (that is, X(0), X(2), . . . ) are transmitted throughthe first transmitting antenna and odd numbered common pilot channelsymbols are transmitted through the second transmitting antenna.

In this case, that is, when there are two transmitting antennas,adjacent data on the frequency domain of two adjacent common pilotchannel symbols experience complete independent fading on the frequencydomain.

Here, when a differential multiplication is performed between adjacentsymbols at a transmitting end as in Equation 11, detecting efficiencymay be reduced. On the other hand, as illustrated in reference numeral697 in FIG. 30, when the differential correlation according to anembodiment of the present invention is performed, that is, when evennumbered symbols perform the differential multiplication 697-A and evennumbered symbols perform the differential multiplication 697-B, the longPN scrambling code identifier can be detected, regardless of the numberof transmitting antennas of the base station.

In order to reduce complexity, odd numbered data illustrated in Equation10 is ignored and only even numbered data can be used as in Equation 13.

$\begin{matrix}{\sum\limits_{i = 0}^{\frac{N_{p}}{4} - 1}\begin{Bmatrix}\left( {{X\left( {4\; i} \right)}\left( {c_{g_{k}}\left( {4i} \right)} \right)^{\star}} \right) \\\left( {X\left( {{4i} + 2} \right)\left( {c_{g_{k}}\left( {{4i} + 2} \right)} \right)^{\star}} \right)^{\star}\end{Bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

As described above, the initial cell searching process performed by themobile station when a power source is applied to the mobiles station isdescribed. Hereinafter, adjacent cell searching process will bedescribed.

In the cellular system, cell searching process can be classified intoinitial cell searching and adjacent cell searching. The initial cellsearching is performed when the power source is applied to the mobilestation. The adjacent cell searching is performed to detect the frametiming of the adjacent cell having the strong signal and the cellidentifiers, in order to perform handoff in an idle mode or an activemode (or a connected mode) after the initial cell searching iscompleted.

An error rate of the clock generator 540 of the mobile station is closeto 0 in the idle mode or active mode, since frequency offset can becontinuously estimated by using the signal received from the home cell.Therefore, frequency offset does not need to be corrected in second andthird cell searching processes during adjacent cell searching.

In the case of Wideband Code Division Multiple Access (WCDMA), 10 msecframe timing in all base station is independent. That is, WCDMA is anasynchronous cellular system in which base stations are synchronous. Onthe other hand, IS-95 or CDMA 2000 is a synchronization cellular systemin which all base stations are operated by synchronizing with GPS.

In OFDM system, OFDM method is basically used in a forward link. In thiscase, there are two types of services which are MBMS service and unicastservice.

The unicast service may be operated asynchronously between adjacentcells, however, the MBMS service should be operated synchronouslybetween the cells. In this case, that is, in the case of synchronousbase station, the timing difference between OFDM symbols of the signalreceived from the cells adjacent to the cell boundary is smaller thanthe cyclic prefix section. Then, orthogonality can be maintained betweenthe subcarriers of the signal received from the adjacent base stations.

As described above, in the OFDM system, all cells may be operatedsynchronously or synchronous and asynchronous may be co-exist accordingto a wireless communication service provider.

In the OFDM cellular system, when all base stations are operated in abase station synchronization mode, the first adjacent cell searching canbe excluded during adjacent cell searching. That is, 10 msec frameboundary of the signal received from the adjacent cell is within anerror range of the frame boundary of the home cell and cyclic prefix sothat the synchronization and group detecting unit 620 does not need tobe operated. On the other hand, the hopping code detecting unit 640 andthe cell identifier detecting unit 680 should be operated.

Therefore, when the mobile station identifies whether all base stationin the cellular system where the mobile station belongs to is operatedsynchronously, cell searching can be easily performed. Accordingly, thebase station according to the present invention sends information onwhether all base station in the current cellular system is operatedsynchronously to all mobile station in the cell through a broadcastingchannel of a forward link or a control channel.

For example, 1 bit is set in a message part of the broadcasting channelas a “system synchronization identifier” and the mobile station isinformed that when the value is 1, all base station in the currentcellular system is operated synchronously and when the value is 0, apart of the base station in the current cellular system is operatedsynchronously. When such value is 0, the base station operatedsynchronously for the MBMS service may exist (that is, a synchronizationbase station and an asynchronous base station may co-exist).

When the system synchronization identifier is 0 and 1, a cell searchingalgorithm of the mobile station may change. As mentioned above, when thesystem synchronization identifier is 1, that is, all base station isoperated synchronously, the first cell searching process may not beneeded.

On the other hand, when the system synchronization identifier is 0, thehome cell (or serving cell) in which the current mobile station isincluded may be operated asynchronously. Also, since the home cell is ina synchronization mode and a cell among the adjacent cells may beoperated in an asynchronous mode, all cell searching process includingthe first cell searching process may be required.

Whether the home cell and the adjacent cells are operated in asynchronization mode can be known according to whether each base stationof the cellular system is operated in a synchronization mode, that is,whether the “home cell synchronization mode identifier” and the adjacentbase stations are operated in a synchronization mode, that is, “adjacentcell synchronization mode identifier”, is transmitted to the mobilestation included in the cell through a broadcasting channel or a controlchannel.

Only one home cell synchronization mode identifier is needed, however,various number of the adjacent cell identifiers are needed, since theadjacent cell identifiers should provide information on the cellsexisting around the current base station. The mobile station canefficiently search for the adjacent cells in the system, where the cellsoperated in a synchronization mode and the cells operated in anasynchronous mode co-exist, by using the home cell synchronizationidentifier and the adjacent cell synchronization mode identifiers.

In order to support handover without cutting off in the cellular system,the mobile station should search for the adjacent cells, even when thepower of the reception signals in the adjacent base stations is the sameor less than the power of the reception signals in the home cell. Thatis, the mobile station should continuously measure the size of thesignals of the adjacent cells in an idle mode and an active mode andreport to the base station.

In this case, when two adjacent base stations are operated in asynchronization mode, a synchronization channel signal received from thehome cell and a synchronization channel signal received from theadjacent base stations are piled in the time domain and entered so thatwhen the second cell searching process used in the initial cellsearching process is used, the performance thereof may be decreased.

As mentioned above, the mobile station can identify whether the homecell and adjacent cells are operated synchronously from the systemsynchronization identifier, home cell synchronization mode identifier,or adjacent cell synchronization mode identifier.

The adjacent cell searching method of the mobile station according tothe present invention is to insert a block for removing home cellcomponent to a back end of the combiner 656 of FIG. 26 in the secondcell searching process.

FIG. 31 is a block diagram of the sub-group and the boundary detectingunit 650 according to another embodiment of the present invention. InFIG. 31, the sub-group and boundary detector 650 further includes a homecell component removing unit 830. The home cell component removing unit830 removes home cell component from among the output of the combiner656. That is, the correlation value with respect to the synchronizationchannel sequence corresponding to the home cell is replaced to apredetermined number. Here, the predetermined number can be ‘0.’ Sincethe mobile station identifies the hopping code word of the current homecell, the home cell component can be removed.

FIGS. 32A and 32B illustrate an operation of the home cell componentremoving unit 830.

FIG. 32A is an input of the home cell component removing unit 830. Thatis,

FIG. 32A illustrates the result of the correlation between allsynchronization channel sequences used in the system with respect toeach of five received synchronization channel symbols. In FIG. 32A, thehopping code words of the home cell are {4, 5, 6, 7, 8}. In this case,the home cell component removing unit 830 replaces the correlation valuecorresponding to {4, 5, 6, 7, 8} with a small value, for example, 0.

FIG. 32B is an output of the home cell component removing unit 830. InFIG. 32B, the correlation values corresponding to the home cellcomponents, 4, 5, 6, 7, 8 are replaced with 0. Therefore, the code worddetecting unit 658 detects one or more hopping code words except for thehopping code words of the home cell. During the adjacent cell searching,the code word detecting unit 658 minimizes an effect of the home cellcomponent so that the performance of the adjacent cell searching can beimproved.

Meanwhile, when the home base station and the adjacent base station areoperated in a synchronization mode, the code word detecting unit 658does not need to detect the cyclic shift index of the adjacent cellduring the adjacent cell searching process. As described above, since 10msec frame synchronization is set for the home base station and theadjacent base station, the framing timing of the adjacent cells is thesame as the frame timing of the home cell.

In the third adjacent cell searching, the same method used in theinitial cell searching process is basically used, except that thefrequency offset is not corrected. Of course, in the case of the third,fourth, and sixth methods of allocating a code (FIGS. 3, 4, and 5B)where the sub-groups are one-to-one mapped to the cell identifiers, thethird cell searching process may not be needed.

Meanwhile, in the cellular system operated in a base stationsynchronization mode, in order to minimize the power consumption, themobile station can introduce two-step discontinuous reception (DRX) modewhich turns the operation of the receiver including the down converteron/off in a Macroscopic DRX 950 and a Microscopic DRX mode 960 as inFIG. 33, except for the basic clock generator including 10 msec frameclock synchronized with the 10 msec frame boundary 150 of the currentcell, during frequency tracking, fine time tracking, or adjacent cellsearching of the signal in the home cell in an idle mode of the mobilestation.

FIG. 33 is a diagram for explaining a gating mode of the mobile stationduring adjacent cell searching in an idle mode according to anembodiment of the present invention. Firstly, the mobile stationreceives a system parameter from the base station and sets a period ofthe Macroscopic DRX mode. Then, only when the Macroscopic DRX mode is on(952), the mobile station performs frequency tracking or fine timetracking of the signal in the home cell by using the synchronizationchannel and the common pilot channel, in order to demodulate a pagingchannel received from the home cell, or the mobile station searches forthe adjacent cells by using the synchronization channel and the commonpilot channel when the signal component of the home cell is low.

However, in order to reduce the battery consumption of the mobilestation even when the Macroscopic DRX mode is on (952), the MicroscopicDRX mode 960 exists as in FIG. 33. That is, only when the Microsopic DRXis on (900), frequency tracking, time tracking, or adjacent cellsearching is performed and when the Microsopic DRX is off (901),receiving operations of the transmitting end such as adjacent cellsearching and down converting are not performed.

That is, the receiver is turned on only in the predetermined section 900including the synchronization channel symbols and the common pilotchannel and is turned off in other sections so that the cell searchingapparatus is operated by using the received signal in the section wherethe receiver is turned on. Therefore, the mobile station can reducebattery consumption compared with when only the Macroscopic DRX mode isused.

The invention can also be embodied as computer readable codes on acomputer readable recording medium. The computer readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of the computer readablerecording medium include read-only-memory (ROM), random-access-memory(RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storagedevices, and carrier waves. The computer readable recording medium canalso be distributed over network coupled computer system so that thecomputer readable code is stored and executed in a distributed fashion.While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims

1-46. (canceled)
 47. A method of generating a forward link frame in acommunication system in which a plurality of cells are grouped into aplurality of cell groups, and each cell group includes at least twocells, the method comprising: generating a secondary synchronizationsignal for identifying a cell group; generating a primarysynchronization signal for identifying a cell in the cell groupcorresponding to the secondary synchronization signal; and generatingthe forward link frame using the secondary synchronization signal andthe primary synchronization signal.
 48. The method of claim 47, whereineach cell belongs to only one of the plurality of cell groups.
 49. Themethod of claim 47, wherein the forward link frame comprises a pluralityof symbols in a time domain, and the primary synchronization signal andthe secondary synchronization signal are mapped to two adjacent symbols.50. The method of claim 47, wherein the forward link frame comprises aplurality of symbols in a time domain, and the primary synchronizationsignal is repeatedly disposed on at least two symbols.
 51. The method ofclaim 47, wherein the forward link frame comprises a plurality ofsymbols in a time domain, the secondary synchronization signal isdisposed on each of at least two symbols, and secondary synchronizationsignals disposed on the different symbols are different from each other.52. An apparatus for generating a forward link frame in a communicationsystem in which a plurality of cells are grouped into a plurality ofcell groups, and each cell group includes at least two cells, theapparatus comprising: means for generating a secondary synchronizationsignal for identifying a cell group; means for generating a primarysynchronization signal for identifying a cell in the cell groupcorresponding to the secondary synchronization signal; and means forgenerating the forward link frame using the secondary synchronizationsignal and the primary synchronization signal.
 53. The apparatus ofclaim 52, wherein each cell belongs to only one of the plurality of cellgroups.
 54. The apparatus of claim 52, wherein the forward link framecomprises a plurality of symbols in a time domain, and the primarysynchronization signal and the secondary synchronization signal aremapped to two adjacent symbols.
 55. The apparatus of claim 52, whereinthe forward link frame comprises a plurality of symbols in a timedomain, and the primary synchronization signal is repeatedly disposed onat least two symbols.
 56. The apparatus of claim 52, wherein the forwardlink frame comprises a plurality of symbols in a time domain, thesecondary synchronization signal is disposed on each of at least twosymbols, and secondary synchronization signals disposed on the differentsymbols are different from each other.
 57. A method of searching a cellin a mobile station of a communication system in which a plurality ofcells are grouped into a plurality of cell groups, and each cell groupincludes at least two cells, the method comprising: detecting asecondary synchronization signal and a primary synchronization signalfrom a received signal, identifying a cell group to which the mobilestation belongs among the plurality of cell groups based on thesecondary synchronization signal; and identifying a cell to which themobile station belongs among at least two cells within the identifiedcell group based on the primary synchronization signal.
 58. The methodof claim 57, wherein each cell belongs to only one of the plurality ofcell groups.
 59. The method of claim 57, wherein a frame of the receivedsignal comprises a plurality of symbols in a time domain, and theprimary synchronization signal and the secondary synchronization signalare mapped to two adjacent symbols.
 60. The method of claim 57, whereina frame of the received signal comprises a plurality of symbols in atime domain, and the primary synchronization signal is repeatedlydisposed on at least two symbols.
 61. The method of claim 57, wherein aframe of the received signal comprises a plurality of symbols in a timedomain, the secondary synchronization signal is disposed on each of atleast two symbols, and secondary synchronization signals disposed on thedifferent symbols are different from each other.
 62. An apparatus forsearching a cell in a mobile station of a communication system in whicha plurality of cells are grouped into a plurality of cell groups, andeach cell group includes at least two cells, the apparatus comprising:means for detecting a secondary synchronization signal and a primarysynchronization signal from a received signal; means for identifying acell group to which the mobile station belongs among the plurality ofcell groups based on the secondary synchronization signal; and means foridentifying a cell to which the mobile station belongs among at leasttwo cells within the identified cell group based on the primarysynchronization signal.
 63. The apparatus of claim 62, wherein each cellbelongs to only one of the plurality of cell groups.
 64. The apparatusof claim 62, wherein a frame of the received signal comprises aplurality of symbols in a time domain, and the primary synchronizationsignal and the secondary synchronization signal are mapped to twoadjacent symbols.
 65. The apparatus of claim 62, wherein a frame of thereceived signal comprises a plurality of symbols in a time domain, andthe primary synchronization signal is repeatedly disposed on at leasttwo symbols.
 66. The apparatus of claim 62, wherein a frame of thereceived signal comprises a plurality of symbols in a time domain, thesecondary synchronization signal is disposed on each of at least twosymbols, and secondary synchronization signals disposed on the differentsymbols are different from each other.
 67. A computer-readable mediumhaving a program stored thereon for executing a method in acommunication system in which a plurality of cells are grouped into aplurality of cell groups, and each cell group includes at least twocells, the method comprising: generating a secondary synchronizationsignal for identifying a cell group; generating a primarysynchronization signal for identifying a cell in the cell groupcorresponding to the secondary synchronization signal; and generating aforward link frame using the secondary synchronization signal and theprimary synchronization signal.
 68. The computer-readable medium ofclaim 67, wherein each cell belongs to only one of the plurality of cellgroups.
 69. The computer-readable medium of claim 67, wherein theforward link frame comprises a plurality of symbols in a time domain,and the primary synchronization signal and the secondary synchronizationsignal are mapped to two adjacent symbols.
 70. The computer-readablemedium of claim 67, wherein the forward link frame comprises a pluralityof symbols in a time domain, and the primary synchronization signal isrepeatedly disposed on at least two symbols.
 71. The computer-readablemedium of claim 67, wherein the forward link frame comprises a pluralityof symbols in a time domain, the secondary synchronization signal isdisposed on each of at least two symbols, and secondary synchronizationsignals disposed on the different symbols are different from each other.72. A method of generating a forward link frame in a communicationsystem in which a plurality of cells are grouped into a plurality ofcell groups, and each cell group includes at least two cells, the methodcomprising: generating a secondary synchronization signal and a primarysynchronization signal; and generating the forward link frame using thesecondary synchronization signal and the primary synchronization signal,wherein one cell group of the plurality of cell groups and one cellwithin the one cell group are identified by a combination of thesecondary synchronization signal and the primary synchronization signal,and the secondary synchronization signal depends on the primarysynchronization signal.
 73. The method of claim 72, wherein the forwardlink frame comprises a plurality of symbols in a time domain, and theprimary synchronization signal and the secondary synchronization signalare mapped to two adjacent symbols.